Methods for isolating surface marker displaying agents

ABSTRACT

The invention relates to method and kits for highly specific isolation of extracellular vesicles (EVs) by targeting at least two EV surface markers. The invention further relates to methods and kits for analyzing EVs and their contents.

FIELD OF THE INVENTION

The invention relates to methods and kits for highly specific isolation and analysis of surface marker displaying agents such as extracellular vesicles (EVs) and/or their cargo by targeting at least two surface markers.

BACKGROUND

Surface marker displaying agents include cells, viruses and viral particles, cellular organelles, and vesicles, including extracellular vesicles (EVs) and exosomes. Surface marker displaying agents may include biologically relevant materials or components; therefore, methods of isolating and/or characterizing various types of surface marker displaying agents are actively being developed and improved.

Extracellular vesicles (EVs) are a diverse group of cell-secreted membrane vesicles implicated in a wide variety of physiological and pathological processes, many of which are only beginning to be understood. These include immune regulation, antigen presentation, tumor progression and metastasis, modulation of inflammation, stem cell regulation, neuronal development and regeneration, and cell-to-cell transfer of pathogenic proteins and nucleic acids. EVs are secreted from nearly all cell types through multiple mechanisms including the fusion of specific endosomal compartments called multivesicular bodies (MVB) with the plasma membrane and by budding/shedding directly from the plasma membrane. EVs are present in nearly all body fluids including blood, urine, cerebral spinal fluid, and saliva, and are secreted by most in vitro cultured cells as well. Because of the EV formation mechanisms, EVs contain specific lipids, membrane proteins, and internalized proteins, nucleic acids and metabolites derived from their cells of origin and are thus a rich source of potential biomarkers.

Recent research suggests a role for EVs in the function of the healthy central nervous system (CNS) as well as a role in numerous diseases of the CNS. Many cells of the CNS including neurons, astrocytes, oligodendroglia and microglia have been shown to secrete EVs in vitro. In neurons, synaptic activity-dependent EV release and reuptake has been observed and has been proposed as a possible mechanism of synaptic plasticity and inter-neuronal transfer of complex information. Neurons have also been shown to transfer miRNA via EVs to astrocytes, modulating the level of an important functional synaptic protein, EAAT2/GLT1. EV secretion by oligodendrocytes has been found to modulate myelin biogenesis, promote neuronal viability under stress and enable degradation of oligodendroglial membrane proteins by a subset of microglia through an “immunologically silent” macropinocytotic mechanism. Astrocyte-derived EVs have been shown to promote neuronal survival under stress by transferring heat-shock proteins and synapsin I. EV secretion by microglia has been shown to be inducible by Wnt-signaling and to stimulate synaptic activity by enhancing sphingosine metabolism in neurons and to represent a unique secretion mechanism for IL-1beta, an important neuroinflammatory cytokine.

In addition to promoting healthy CNS function, EVs appear to play several roles in various CNS diseases and disorders. Broadly these include the export of toxic proteins and possibly promotion of toxic isoform formation, mediation of neuroinflammation, and the transfer of disease associated miRNAs. Numerous studies have demonstrated that EVs can mediate the transfer of toxic proteins between cells both in-vitro and in animal studies. This includes the misfolded prion protein PrPSc, the infectious agent in human diseases Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler-Scheinker syndrome (GSS), aggregated alpha-synuclein, the pathogenic species associated with Parkinson's disease and Lewy body dementia, aggregated Tau and beta-amyloid peptides hallmarks of Alzheimers disease (AD), frontotemporal lobar degeneration (FTD) and progressive supranuclear palsy (PSP), and mutated SOD1, linked to the development of amyotrophic lateral sclerosis (ALS). There is also some evidence that the secretion of toxic proteins in EVs may actually have a protective role, facilitating clearing of these pathogenic species by microglia.

Assessing the composition of EVs and their cargo generally requires isolating a pure population of EVs and separating it from non-EV associated factors. Some demonstrations of this idea have focused on enriching CNS-derived extracellular vesicles (CNS-EVs) from plasma or serum based on immunoaffinity capture of specific EV surface proteins and measuring disease-associated proteins within the enriched EV population.

Despite its utility, this method has significant fundamental and technical drawbacks. Fundamentally, the use of a single marker for EV isolation presents a great challenge. Most surface proteins are expressed on a variety of cell types; thus, multiple markers are usually needed to define a specific cell population. This is often apparent in flow cytometry, wherein multiple markers are usually employed despite the benefit of a predefined input cell population (e.g. PBMCs, or cultured cells). When isolating EVs from blood, nearly all cell types of the organism may be represented within the EV population, increasing the challenge of identifying a single marker specific for EVs from one cell type. Technical challenges of the existing approach are illustrated by the dramatic differences in levels of circulating L1CAM+ EVs and associated cargo molecules (e.g. Tau) reported by multiple groups using nearly identical protocols. This variability, which likely stems from minor variations in protocols from lab to lab (e.g. wash or mixing steps) speaks to the need for protocol standardization and simplification.

SUMMARY OF THE INVENTION

In embodiments, the invention provides a method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; (b). binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

The present invention provides methods of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c) hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; and (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

The invention further provides methods of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; (b). hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

The invention further provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (b). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and (c). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof. In some embodiments, the assay is an ultrasensitive assay.

The invention additionally provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV of interest in a sample, comprising: (a). contacting the sample comprising an EV with a surface, wherein the EV encapsulates a protein, a nucleic acid, a lipid, or a combination thereof, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and anchoring oligonucleotide; and (d). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof. In embodiments, the assay is an ultrasensitive assay.

The invention further provides kits for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring reagent; and (b) a binding reagent for the EV.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention.

FIGS. 1A-1E—example of the “EV Stapling” method for multi-marker EV isolation. FIG. 1A: Capture antibodies are displayed on the plate surface using labile linker. EVs are captured via the first surface marker. The second surface marker is then decorated by an oligonucleotide-labeled antibody that serves as amplification primer. FIG. 1B: When this primer is present on captured EVs, rolling circle amplification can occur. An additional sequence in the circular template produces a “staple sequence” which hybridizes to complementary oligonucleotides on the surface, “stapling” the EV down to the surface. A typical amplification reaction may produce many copies of the staple sequence yielding a highly stable complex. FIG. 1C: The labile linker is denatured, releasing capture antibodies from the surface. EVs that are stapled remain surface-bound, while those that lacked the second surface marker and thus were not stapled are eluted from the surface and washed away. FIG. 1D: The stapling technique was demonstrated on cell culture derived EVs known to express high levels of CD9 and CD81 and low levels of CD63. EVs were captured with a CD9 antibody followed by stapling with CD81, CD63 or irrelevant antibody or no stapling at all. Captured EVs were detected with CD9 antibodies before and after elution. CD81 stapling resulted in complete retention of EVs, while CD63 resulted in retention of a fraction of the EVs. Irrelevant control and no stapling allowed elution of most of the captured EVs. Optimization will be needed to achieve close to 100% elution for these control conditions. FIG. 1E: Schematic of example of three marker isolation.

FIG. 2A is a schematic of an example of a 3 marker EV sandwich assay: Specific capture antibody(s) are displayed on the surface of MSD ECL plates. EVs are captured and then detected with two oligonucleotide-labeled antibodies. Typically, one of these targets a common EV surface marker while the other targets a second EV population specific marker. All three antibodies must bind to the same EV to generate an assay signal. FIG. 2B. Effect of replacing each antibody in three marker assay with irrelevant control antibodies. Assays were performed on cell culture derived EVs with distinct antigens for the three antibody targets.

FIG. 3 is a schematic of an example where captured EVs are tethered to surface with a “staple” (linker) oligonucleotide.

FIG. 4 is a schematic of an example of Assaying EV Cargo: FIG. 4A. Cell culture EVs are captured on affinity capture plate with EV-specific or irrelevant antibodies and washed, followed by lysis and transfer to an ultrasensitive assay for EGFR cytoplasmic domain. The supernatant has detectable levels of the analyte outside the EVs (no lysis), but after lysis the signal increases to 3-fold, indicating roughly twice as much analyte within the EVs as outside. Nearly all of the EGFR containing EVs are captured on the CD9 plate, while the CD81 and CD63 only yield about half of the total EV associated EGFR. Very few EVs are captured by the control antibody so the EGFR signal is quite low. FIG. 4B. Cargo proteins can be difficult to measure accurately when the same protein species is abundant in soluble form. A cell conditioned medium with >500-fold more HSP70 in soluble form than in the EV cargo was selected to mitigate the effect of this soluble protein. When the EVs are captured with CD81 antibodies or an irrelevant control antibody and then lysed, a fraction of the soluble HSP70 binds non-specifically to the well and are transferred to the assay plate along with the true cargo, which would lead to an overestimation of the true EV cargo. After proteolysis, only the true EV cargo are transferred to the assay well. When the captured EVs are lysed before protease treatment, all of the cargo is digested as well.

FIGS. 5A-5B show the results of the experiments described in Example 1.1. FIGS. 5A and 5B show ECL signal from tetraspanin (CD63, CD81, and CD9) sandwich assays performed on cell culture media depleted in 2 hours and 4 hours, respectively. Bar graphs represent the depleted fraction, calculated as the difference in signal between fresh media and depleted media as a fraction of the signal from fresh media.

FIGS. 6A-6B show the results of the experiments described in Example 1.2. FIG. 6A shows ECL signal from tetraspanin (CD63, CD81, and CD9) sandwich assays performed on non-eluted wells using various dilutions of capture antibodies. FIG. 6B shows the correlation between the elution efficiency (percent eluted) and capture antibody dilution.

FIG. 7 illustrates an embodiment described in Example 1.2, wherein EVs are captured by labeled capture antibodies immobilized on a solid surface. The EV-capture antibody complex is first eluted from the solid surface, and the capture antibody can then optionally be released from the EV for further characterization, or the EV-capture antibody complex can be used directly in detection assays.

FIG. 8 shows the results of the experiments described in Example 1.3. EVs were captured by bead-based immunoaffinity capture using either CD81 antibody or a non-specific isotype-matched antibody. The EVs were eluted at low pH, and the non-depleted sample, and depleted supernatant sample were evaluated using tetraspanin (CD63, CD81, and CD9) sandwich assays. Bar graph represents the ECL signal from each sample.

FIGS. 9A-9C relate to the experiments described in Example 2.1.1. Calibration curves for tetraspanin (CD63, CD81, and CD9) sandwich assays are shown in FIGS. 9A, 9B, and 9C, respectively. Calibration curves for the assay in diluent A with and without 10% fetal bovine serum (FBS) were generated for each sample.

FIG. 10 relates to experiments described in Example 2.1.2. Calibration curves for tetraspanin (CD63, CD81, and CD9) sandwich assays for exosomes from THP-1 cells are shown.

FIG. 11 shows the results of the experiments described in Example 2.2. Intact EV assays were performed using all pairwise combinations of CD63, CD81, and CD9 as capture and detection antibodies.

FIG. 12 shows the results of the experiments described in Example 2.2.1. Cell conditioned medium from different biological samples and purified EVs (1^(st) column) were evaluated by intact EV assays using all pairwise combinations of CD63, CD81, CD9, and EpCAM as capture and detection antibodies.

FIGS. 13A-13C relate to the experiments described in Example 2.2.2. FIG. 13A illustrates using a tetraspanin capture antibody with an isotype-matched non-specific control antibody as the detection antibody to assess non-specific binding of detection antibodies to specifically captured EVs. FIG. 13B illustrates using isotype-matched non-specific control antibody as the capture antibody with a tetraspanin detection antibody to assess non-specific binding of exosomes to the surface. The results of the intact EV assays in FIG. 13C show low non-specific binding of EVs to IgG1 control capture antibody (last column) and low binding of IgG1 control antibody to captured EVs (4^(th) row).

FIG. 14 relates to the experiments described in Example 2.3.1. Capture antibodies targeting CD63, CD81, and CD9 were displayed within the same well for multiplex assays. Singleplex and multiplex intact EV assays were performed on Expi293 cell conditioned medium, using all pairwise combinations of tetraspanin (CD63, CD81, and CD9) capture and detection antibodies. FIG. 14 shows the ratios of the multiplex signal to the singleplex signal. In most cases, the multiplex assay signal is within 10% of the singleplex assay signal.

FIG. 15 shows the results of the experiments described in Example 2.3.2 (A). Two 8-plex capture multiplexes were used to screen 15 different culture conditions representing 10 different cell lines. Each sample and capture multiplex were used in combination with each of the tetraspanin detectors. Cell lines that produced EVs with 11 of the 13 tumor markers were identified.

FIGS. 16A-16B relate to the experiments described in Example 2.3.2 (B). FIG. 16A shows the results of a 10-plex assay of cell culture control samples with cancer antigen capture antibodies and a triplex of tetraspanin (CD63, CD81, and CD9) capture antibodies. Each sample and capture multiplex was combined with a cocktail of all three tetraspanin detectors to maximize signal. FIG. 16B shows the results of the same 10-plex assay on plasma samples from 10 pancreatic ductal adenocarcinoma patents and 10 healthy subjects.

FIG. 17 shows the results of the experiments described in Example 2.3.2 (C). Samples of cell conditioned media and exosomes from various cell lines and serum pools (1^(st) column) were captured using three 6-plex panels of cancer antigens and detected using a cocktail of tetraspanin (CD63, CD81, and CD9) detection antibodies. Several expected surface markers were detected in pancreatic cancer cell lines.

FIGS. 18A-18B relate to the experiments described in Example 2.4.1 (A). FIG. 18A illustrates a single antibody RCA detection assay of EV-associated antigen. The results of the assay in FIG. 18B show linear amplification across a wide range of dilutions with no observable elevation in background signal.

FIGS. 19A-19C relate to the experiments described in Example 2.4.1 (B). FIG. 19A illustrates a homo-pair proximity ligation/RCA. FIG. 19B illustrates a hetero-pair proximity ligation/RCA. The results of the assays in FIG. 19C demonstrate low non-specific binding and high specific signal for all combinations of proximity probes.

FIG. 20 shows the results of the experiments described in Example 2.4.1 (C). EVs from four cell conditioned medium samples were captured on plates printed with an anti-EphA2 capture antibody. Captured EVs were detected with homo-pairs of proximity probes in a PLA/RCA assay (e.g., CD9/CD9), hetero-pairs (e.g., CD9/CD81), or cocktails comprising CD63, CD81, and CD9 PP1s and CD63, CD81, and CD9 PP2s at two different concentrations.

FIGS. 21A-21B show the results of the experiments described in Example 2.4.2 (A). FIG. 21A is a comparison of singleplex and multiplex PLA/RCA tetraspanin (CD63, CD81, and CD9) assays performed with a blocking step. FIG. 21B is a comparison of singleplex and multiplex PLA/RCA assays performed without the blocking step.

FIGS. 22A-22B show the results of the experiments described in Example 2.4.2 (B). Multiplex assays were performed using cell conditioned medium from 12 different cell lines. FIG. 22A shows the assay results using a multiplex capture panel containing 6 proteoglycan surface markers and the isotype control. FIG. 22B shows the assay results using a multiplex capture panel containing 5 cell adhesion proteins and 2 surface receptors and the isotype control.

FIG. 23 illustrates a method for assaying EV cargo proteins as described in Example 3.

FIGS. 24A-24C show the results of the experiments described in Example 3.1.1.

FIG. 24A compares IL-6 levels in cell conditioned medium from wild-type and transfected Expi293 cells. FIG. 24B shows the results of IL-6 assays on captured EVs to determine whether the IL-6 was present in the exosome. FIG. 24C shows the levels of non-specific binding of soluble IL-6 in the assays of captured EVs.

FIGS. 25A-25C show the results of the experiments described in Example 3.1.2. FIG. 25A shows the results of an ultrasensitive assay for EGFR (cytoplasmic domain) with and without lysis. FIG. 25B shows a calibration curve for the EGFR cytoplasmic domain assay. FIG. 25C shows the results of an ultrasensitive assay for EGFR cytoplasmic domain from captured and lysed EVs.

FIGS. 26A-26C relate to the experiments described in Example 3.2. FIG. 26A illustrates the procedure of an enzymatic digestion of non-cargo proteins in an EV-containing sample. FIG. 26B shows the results of an immunoassay of captured EVs detecting for EV-cargo HSP70. FIG. 26C shows the results of an immunoassay of captured EVs detecting for EV-cargo IL-6.

FIGS. 27A-27B relate to the experiments described in Example 3.3. FIG. 27A illustrates the procedure of fixing and permeabilizing captured EVs. Results in FIG. 27B show the effect of fixation and permeabilization on the detection of HSP70 in captured EVs.

FIG. 28 shows the results of the experiments described in Example 4. MSD Read Buffer B with varying concentrations of TRITON X-100 and Tween-20 were tested in EV assays using tetraspanin (CD63, CD81, and CD9) and isotype control capture antibodies and CD81 detection antibody.

FIG. 29 shows the results of the experiments described in Example 5.1. EV assays were performed on four different samples sets using all combinations of tetraspanin (CD63, CD81, and CD9) and EpCAM capture and detection antibodies.

FIGS. 30A-30B show the results of the experiments described in Example 5.2. FIG. 30A shows the ECL signal from EV-associated tetraspanins (CD63, CD81, and CD9) in cell conditioned medium from THP-1 cells. FIG. 30B shows nanoparticle tracking analysis results of EVs in THP-1 cell culture.

FIGS. 31A-31C illustrate a method for determining EV surface markers as described herein. FIG. 31A shows an EV bound to three antibodies from a pool of antibodies (not shown). At least one antibody is biotinylated, allowing the EV to be captured on a streptavidin bead, and washed to remove unbound EVs and antibodies. Extension and ligation reagents are added to ligate and join the barcodes into a single oligonucleotide. FIG. 31B shows the barcode screening process for EV surface markers. For screening, sequencing adapters are added by PCR, and each 3-barcode combination is read by next-generation sequencing. FIG. 31C shows the isolation process, which includes cleaving the first restriction endonuclease site (“RS1”). After cleavage at RS1, only the EVs tethered by the extension/ligation process are retained on the streptavidin bead, and non-specifically-bound EVs or other undesired components are removed by washing. Finally, retained EVs are eluted by cleaving at the second restriction endonuclease site (“RS2”), or by eluting from the antibodies at low pH.

FIG. 32 illustrates an exemplary method of isolating an EV of interest from a sample using multiple (e.g., three) markers and a single solid phase, as described herein.

FIG. 33 illustrates an exemplary method of isolating two different EV populations of interest from a sample using multiple markers and a single solid phase, wherein the two different EV populations bind to two of the same binding reagents and one different binding reagent, as described herein.

FIG. 34 illustrates an exemplary method of isolating two different EV populations of interest from a sample using multiple markers and a single solid phase, wherein the two different EV populations bind to one of the same binding reagents and two different binding reagents, as described herein.

FIG. 35 illustrates an exemplary method of isolating two different EV populations of interest from a sample using multiple markers and a single solid phase, wherein the two different EV populations bind to three different binding reagents, as described herein.

FIG. 36 illustrates another exemplary method of isolating two different EV populations of interest from a sample using multiple markers and a single solid phase, wherein the two different EV populations bind to three different binding reagents, as described herein.

FIGS. 37A and 37B relate to Example 12. FIG. 37A shows the results of an EV assay used to compared EV secretion from various cell lines in different cellular states. FIG. 37B shows the results of an EV assay used to compare multiple growth or stimulation conditions on a single cell line, THP-1.

FIG. 38 relates to Example 13. FIG. 38 shows results of an EV assay with different biofluid samples spiked with EV: human serum, plasma, CSF, and urine.

FIGS. 39A and 39B relate to Example 14. FIG. 39A shows a dilution curve for a two-marker EV assay for all combinations of CD63, CD81, and CD9 capture and detection antibodies. FIG. 39B shows the results of a single-marker and two-marker EV assays to compare EV subpopulation abundance and relative levels of each EV-associated marker.

FIG. 40 relates to Example 15. FIG. 40 shows the results of single-marker and two-marker EV assays to determine assay performance with matched serum and plasma samples.

FIG. 41 relates to Example 16. FIG. 41 shows the results of a comparison of singleplex and multiplex EV assays.

FIGS. 42A and 42B relate to Example 17. FIG. 42A shows the results from the development of an EV-marker screening panel in a multiplex format. FIG. 42B shows panels of markers that were screened.

FIGS. 43A and 43B relate to Example 18. FIGS. 43A and 43B show the results of an EV assay for EVs captured from cell conditioned medium using the antibody panels from FIG. 42B.

FIG. 44 relates to Example 19. FIG. 44 shows the results of an EV assay for EVs captured from human biofluids using the antibody panels from FIG. 42B.

FIG. 45 relates to Example 20. FIG. 45 shows the results of the cluster analysis of the EV screening data from Examples 18 and 19.

FIGS. 46 and 47 relate to Example 4.1. FIG. 46 shows the signal change in an EV assay based on the read buffer type and concentration of TRITON X-100. FIG. 47 shows a titration curve for known concentrations of EV tested with two different lots of MSD read buffer A.

DETAILED DESCRIPTION OF THE INVENTION I. Overview

The present disclosure provides methods of isolating and/or characterizing surface marker displaying agents. Surface marker displaying agents can be naturally-occurring, partially synthetic, or fully synthetic. In embodiments, a surface marker displaying agent is a biologically relevant material or component. In general, a surface marker displaying agent comprises a surface, typically a lipid bilayer, membrane, cell wall, or envelope, on which one or more markers are displayed. In embodiments, the surface marker displaying agent encapsulates components such as, e.g., proteins, nucleic acids, lipids, carbohydrates, small molecules such as hormones, cofactors, vitamins, minerals, salts, metals, metal-containing compounds, or combination thereof. Examples of surface marker displaying agents include cells (including prokaryotic cells such as bacterial cells or archaeal cells; eukaryotic cells such as mammalian cells, insect cells, or plant cells); viruses and viral particles; cellular organelles such as nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, vacuoles, or chloroplast; vesicles such as lysosome, endosome, peroxisome, and liposome; and extracellular vesicles (EVs) or exosomes.

A variety of analytical methods have been used to characterize EVs and their encapsulated contents (i.e., cargo) including, most commonly, immunoassays (Western blotting, flow cytometry, sandwich immunoassays), electron microscopy, mass spectrometry, PCR and sequencing, and nanoparticle tracking. One of the most significant limitations to characterizing EVs has been the difficulty of separating EVs from the other components in complex biofluids.

EV isolation, enrichment, and purification have been the subject of extensive discussion and publication yet there is still not one universally-accepted method. Ultracentrifugation, ultrafiltration, size-exclusion chromatography, and immuno-affinity based methods all have their strengths and shortcomings. Each must be applied in the appropriate situation with full recognition of the potential for introducing bias or allowing contamination by non-EV components of the sample. Analytical methods that avoid pre-purification steps are advantageous as they introduce no bias in the EV population subject to analysis; however, they have the highest risk of negative effects due to non-EV related molecular interactions and artifacts.

The inventors have discovered a surprisingly effective and highly specific method of isolating EVs of interest from samples. In embodiments, and by way of example, the method indirectly attaches an EV to a surface using at least two separate EV surface markers. In embodiments, first, an EV is indirectly attached to a surface using an EV surface marker, then a second indirect attachment point is formed by way of a second EV surface marker. In embodiments, following removal of unwanted components, the first indirect attachment point is broken, leaving the EV indirectly attached to the surface by only the second surface marker. In this way, EVs not having either surface marker, or EVs having only the first surface marker, are also released from the surface, leaving only EVs having both markers.

II. Methods

In embodiments, the invention provides a method of isolating a surface marker displaying agent of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; (b). binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest.

In embodiments, the surface marker displaying agent is a cell. In embodiments, the cell is a prokaryotic cell such as, e.g., a bacterial cell or an archaeal cell. In embodiments, the cell is a eukaryotic cell such as, e.g., a mammalian cell, an insect cell, or a plant cell. In embodiments, the cell is a human cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the organelle is a nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, vacuoles, or chloroplast. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the vesicle is a lysosome, endosome, peroxisome, liposome, extracellular vesicle, or exosome. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments, the invention provides a method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; (b). binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

In embodiments, the anchoring reagent indirectly binds to the binding reagent. In embodiments, the anchoring reagent is releasably bound to the binding reagent. In embodiments, the intermolecular force by which the capture reagent is releasably bound to the surface is different than the intermolecular force by which the anchoring reagent is releasably bound to the binding reagent. Thus, in embodiments, releasing the capture reagent from the surface does not cause release of the anchoring reagent from the binding reagent, and vice versa.

In embodiments, the binding reagent comprises an antibody or antigen binding fragment thereof, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer. Thus, the binding reagent/anchoring reagent pairs comprise antibody or antigen binding fragment thereof/antigen or epitope or hapten or mimotope, antigen/antibody or antigen binding fragment thereof ligand/receptor, receptor/ligand, oligonucleotide/oligonucleotide, hapten/antibody or antigen binding fragment thereof, epitope/antibody or antigen binding fragment thereof, mimitope/antibody or antigen binding fragment thereof, or aptamer/target molecule. In embodiments, the binding reagent is an antibody comprising a primer oligonucleotide and the anchoring agent comprises an oligonucleotide. In embodiments, the binding reagent comprises streptavidin or biotin. In these embodiments, the anchoring reagent comprises biotin or streptavidin, respectively. Alternatively, both the binding reagent and the anchoring reagent comprise biotin, and streptavidin or avidin act as a bridging reagent for the two.

In embodiments, the anchoring reagent comprises an oligonucleotide, aptamer, aptamer ligand, antibody, antigen, ligand, receptor, hapten, epitope, or mimetope. Thus, the anchoring reagent/binding reagent pairs comprise an oligonucleotide/oligonucleotide, aptamer/aptamer ligand, aptamer ligand/aptimer, antibody/antigen or hapten or epitope or mimotope, antigen/antibody or antigen binding fragment thereof, ligand/receptor, receptor/ligand, hapten/antibody or antigen binding fragment thereof, epitope/antibody or antigen binding fragment thereof, or mimetope/antibody or antigen binding fragment thereof. In embodiments, the anchoring reagent comprises an oligonucleotide and the binding reagent comprises an oligonucleotide. In embodiments, the anchoring reagent comprises streptavidin or biotin. In these embodiments, the binding reagent comprises biotin or streptavidin, respectively. Alternatively, both the binding reagent and the anchoring reagent comprise biotin, and streptavidin or avidin act as a bridging reagent for the two.

Thus, in embodiments, the anchoring reagent is directly or indirectly bound to the surface. In embodiments, the anchoring reagent is releasably or unreleasably bound to the surface.

In further embodiments, the binding reagent comprises an antibody or antigen binding fragment thereof comprising a primer oligonucleotide that generates an amplicon, and the anchoring reagent comprises an oligonucleotide sequence complementary to the amplicon. In embodiments, the binding reagent comprises streptavidin and the anchoring reagent comprises biotin. In embodiments, the binding reagent comprises biotin and the anchoring reagent comprises streptavidin. Alternatively, both the binding reagent and the anchoring reagent comprise biotin, and streptavidin or avidin act as a bridging reagent for the two.

In additional embodiments, the invention provides a method of isolating a surface marker displaying agent of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the surface marker displaying agent, the binding reagent and the anchoring oligonucleotide; and (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest.

In additional embodiments, the invention provides a method of isolating a surface marker displaying agent of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the surface marker displaying agent, the binding reagent and the anchoring oligonucleotide; and (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest.

In embodiments, the invention further provides a method of isolating a surface marker displaying agent of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; (b). hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the surface marker displaying agent, the binding reagent and the anchoring oligonucleotide; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest.

In embodiments, the unwanted components include surface marker displaying agents that bind to the capture reagent, but not the binding reagent. In the methods of the invention, surface marker displaying agents that bind to the capture reagent, but not the binding reagent, will be eluted following releasing the capture reagent from the surface. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In additional embodiments, the invention provides a method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent and the anchoring oligonucleotide; and (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

In embodiments, the methods provided herein are generally applicable to isolation of any surface marker displaying agent of interest. In embodiments, the methods provided herein are also generally applicable to isolation of any EV of interest, such as tissue or organ or cell-type specific EVs. In embodiments, the methods use a high throughput 96-well plate format using a single immunoaffinity capture step, followed by a process termed “stapling” or, in the case of EVs, “EV-stapling.” In embodiments, the methods use particles, e.g., beads, as a solid phase, followed by stapling. This process uses specific recognition of one or multiple oligo-labeled detection antibodies to template the formation of a ssDNA amplicon that tethers surface marker displaying agents, e.g., EVs, to the surface through formation of multiple identical dsDNA duplexes, termed “staples.” Those surface marker displaying agents, e.g., EVs, that were not stapled can then be removed from the surface, thus selectively enriching the surface marker displaying agents, e.g., EVs, of interest.

A schematic representation of the “EV-stapling” process is depicted in FIGS. 1A-1C. FIG. 1E shows schematically how this approach uses three markers with the introduction of a ligation site in the circular oligo template and a third antibody conjugated to a splint oligo, akin to the 3-marker assays shown in FIG. 2. In embodiments, four or more antibodies are used, using additional ligation sites and splint-labeled antibodies. Once the non-stapled EVs are removed, in embodiments, the stapled EVs are assayed in situ using an ECL labeled detector antibody. In embodiments, then they are either lysed to assess their cargo, or they may be eluted intact for further off-line characterization.

In summary, the methods provided herein provide high-throughput isolation of very specific populations of surface marker displaying agents, e.g., EVs, from large numbers of samples in parallel, in situ assessment of the surface marker displaying agents, e.g., EVs, isolated from each sample, and compatibility with most downstream analytical techniques.

Isolating specific EVs, such as CNS derived EVs, is important to both understanding the intercellular trafficking of pathogenic proteins via EVs and in identifying highly specific biomarkers of pathogenesis in neurodegenerative diseases. While most existing isolation techniques are difficult to scale to very large sample numbers, particularly those that require centrifugation or chromatography, the methods provided by the invention, in embodiments, are inherently scalable and amenable to automation.

In embodiments, the method of the invention comprises binding the EV to two to ten binding reagents, wherein one binding reagent comprises a primer oligonucleotide, wherein the primer oligonucleotide binds to a circular oligonucleotide template and wherein the remainder of the binding reagents comprise splint oligonucleotides required to assemble the circular template.

In embodiments, the invention further provides a method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (b). hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent and the anchoring oligonucleotide; and (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest. This embodiment of the method is exemplified in FIG. 3.

As used herein, the term “isolating” a surface marker displaying agent of interest means to have no more than 5% by weight of any other non-surface marker displaying agents (i.e., unwanted components), and preferably no more than 4%, 3%, 2% or 1% by weight of unwanted components, or preferably no more than 0.8%, 0.6%, 0.4%, 0.2% or 0.1% or less by weight of the unwanted component. In the context of EVs, the term “isolating” an EV of interest means to have no more than 5% by weight of any other non-EV components (i.e., unwanted components), and preferably no more than 4%, 3%, 2% or 1% by weight of unwanted components, or preferably no more than 0.8%, 0.6%, 0.4%, 0.2% or 0.1% or less by weight of the unwanted component. The term “isolating” also encompasses amounts of unwanted components that are undetectable by current methods for detecting such components. As used herein, the term “isolating” is synonymous with enriching and purifying.

Surface Marker Displaying Agents of Interest

Surface marker displaying agents include naturally occurring, partially synthetic, or fully synthetic agents. In embodiments, the surface marker displaying agent is a biologically relevant material or component. In general, a surface marker displaying agent comprises a surface, typically a lipid bilayer, membrane, cell wall, or envelope, on which one or more markers are displayed.

In embodiments, the surface marker displaying agent encapsulates components such as, e.g., proteins, nucleic acids, lipids, carbohydrates, small molecules such as hormones, cofactors, vitamins, minerals, salts, metals, metal-containing compounds, or combination thereof. Examples of surface marker displaying agents include cells (including prokaryotic cells, such as bacterial cells or archaeal cells; eukaryotic cells such as mammalian cells, insect cells, or plant cells); viruses and viral particles; cellular organelles such as nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, vacuoles, or chloroplast; vesicles such as lysosome, endosome, peroxisome, and liposome; and extracellular vesicles (EVs) or exosomes.

In embodiments, the methods provided herein enable capture of a surface marker displaying agent of interest from a sample, wherein the surface marker displaying agent of interest includes a unique co-localization of surface markers. In embodiments, certain markers can exclude unwanted populations of surface marker displaying agents (e.g., use of a mammalian cell-specific marker to exclude non-mammalian cells).

In embodiments, the surface marker displaying agent is a cell, and the methods provided herein enable isolation and/or characterization of a cell of interest in a population of cells. In embodiments, the cell is a bacterial cell. In embodiments, the cell is an archaeal cell. In embodiments, the cell is a eukaryotic cell. In embodiments, the cell is a mammalian cell. In embodiments, the cell is an animal cell. In embodiments, the cell is a human cell. In embodiments, the cell is an insect cell. In embodiments, the cell is a plant cell. In embodiments, the cell is a yeast cell. In embodiments, the cell is a variant of a particular cell type. For example, the methods provided herein can be used to isolate abnormal cells, e.g., a cancer cell, from a sample of tissue or bodily fluid, for example, blood (e.g., comprising a mixture of cancer and non-cancer cells). In another example, the methods provided herein can be used to isolate a specific type of bacteria from a mixed bacterial sample, e.g., an environmental sample.

In embodiments, the methods provided herein enable identification of populations of cells in a sample. In embodiments, a large number of detection reagents for different surface markers can be screened in a single panel to determine all combinations of the surface markers present on the cells. In one example, a single panel can include antibodies to a selected number of CD markers, each antibody conjugated with a unique oligonucleotide as described herein. In embodiments, a single panel includes antibodies to all 350 CD markers. The unique oligonucleotides can be ligated upon formation of a complex between the cell of interest and the antibodies for the desired number of surface markers (e.g., three surface markers). The ligated oligonucleotides can then be sequenced to identify all cells having the three surface markers. Compared with conventional methods of cell isolation and identification using surface markers that rely upon a fluorescence or colorimetric output such as, e.g., flow cytometry, the present methods provide higher efficiency, e.g., by reducing processing and increasing throughput.

In embodiments, the surface marker displaying agent is a virus or viral particle, and the methods provided herein enable isolation and/or characterization of a particular type of virus or viral particle. The present methods may facilitate the study of viruses or viral particles, as traditional methods (for example, flow cell-based methods) may not be able to accurately distinguish between different small viruses or viral particles.

In embodiments, the surface marker displaying agent is a cellular organelle, and the methods provided herein enable isolation and/or characterization of an organelle of interest from a sample. Organelle isolation typically involves multiple rounds of subcellular fractionation and screening. The present methods may advantageously isolate an organelle of interest by using one or more surface markers unique to the organelle of interest. For example, TGN38 is a marker unique to the Golgi; VDAC1 is a marker unique to the mitochondria; cytochrome c reductase is a marker unique to the endoplasmic reticulum; and NUP98 is a marker unique to the nucleus.

In embodiments, the surface marker displaying agent is a vesicle, and the methods provided herein enable isolation and/or characterization of a vesicle of interest from a sample. In embodiments, the vesicle is a lysosome, an endosome, or a peroxisome. Examples of lysosome-specific markers include, e.g., LAMP1, LC3, and ATG5. Examples of endosome-specific markers include, e.g., EEA1, Rab5, Rab7, and palladin. An example of a peroxisome-specific marker is catalase. In embodiments, the vesicle is a liposome. Liposomes can be artificial vesicles that include engineered surface markers.

In embodiments, the vesicle is an extracellular vesicle (EV) or an exosome. EVs are described herein.

Extracellular Vesicles of Interest

EVs released from a variety of cells target recipient cells for intercellular communication and transfer a subset of genetic materials, proteins, lipids, and metabolites. EVs include a broad spectrum of vesicles secreted by several types of cells and the term is used as a collective one. These include exosomes, ectosomes, oncosomes, shed vesicles, microvesicles, and apoptotic bodies. Thus, EVs represent a broad spectrum of vesicles secreted by several types of cells. Major groups include exosomes (endosomal origin, 40-200 nm), microvesicles/ectosomes (plasma membrane origin, 100-1000 nm) and larger particles such as large-oncosomes (tumor cell origin, >1 um). The exact definition and nomenclature for each of these general vesicles classes has yet to be fully codified by the field due to their heterogeneous nature, herein, the term “EVs” is as defined by the International Society of Extracellular Vesicles (see Gardiner et al., Journal of Extracellular Vesicles 5(1):32945 (2016).

The isolation and assay methods provided herein enable capture of EVs of interest from the sample, wherein the EVs bear a unique co-localization of surface markers. In embodiments, certain markers can exclude certain unwanted populations of EVs (e.g., use of CD81 as detection marker to exclude platelet derived vesicles). In embodiments, some of the cell-type specific surface markers select EVs of particular origin (i.e. exosomes or ectosomes/microvesicles). In embodiments, the isolation methods exclude very large EVs, apoptotic bodies and cell debris from cell culture supernatants using common techniques like differential centrifugation, ultrafiltration and size-exclusion chromatography but do not otherwise distinguish between small EVs of various origin.

While EVs secreted by neurons and various glial populations have been studied in vitro, isolating populations of EVs from biofluids remains elusive because no method of discriminating these cell-specific EVs has yet been developed. This invention provides methods of isolating populations based on the fact that combinations of surface markers define EVs secreted by specific cells such as CNS cells. The methods described herein thus take advantage of the fact that most proteins that are highly expressed on the surface of a particular cell line are also present on the surface of the EVs secreted in cultures of those cells. EVs of interest include cells of the CNS, such as neurons and astrocytes.

In embodiments, the EV of interest is secreted from a cell of the central nervous system (CNS). In embodiments, the cell of the CNS is a neuron, an astrocyte, an oligodendrocyte or microglia.

In embodiments, the EV comprises a surface marker that is common to EVs. In embodiments, the first marker is common to EVs. In further embodiments, the marker common to EVs is a tetraspanin. Exemplary tetraspanins include CD9, CD37, CD63, CD 81, and CD82.

In embodiments, the EV comprises a surface marker that is a surface adhesion protein. Exemplary surface adhesion proteins include, but are not limited to, EpCAM, E-Cadherin, P-Cadherin, L1 CAM, NCAM1, Nectin-4, PECAM and ICAM-1. In embodiments, the EV comprises a surface marker that is a surface receptor. Exemplary surface receptors include, but are not limited to, EGFR, EphA2, TFRC, FasR, and TNFR1. In embodiments, the EV comprises a surface marker that is an endothelial marker. Exemplary endothelial markers include, but are not limited to, PECAM, CD276, TEM7, TEM8, and thrombomodulin. In embodiments, the EV comprises a surface marker that is a tumor antigen. Exemplary tumor antigens include, but are not limited to, CEA, CA19.9, CA50, CA125, CA15.3, mesothelin, cytokeratin-8, E-cadherin, EGFR, EpCAM, EphA2, NCAM, P-cadherin, cMET, Flt-3L, TNFR-2, cKit, ErbB2, and ANXA1. In embodiments, the tumor antigen markers are pancreatic cancer markers. In embodiments, the EV comprises a surface marker that is a platelet EV marker. Exemplary platelet EV markers proteins include, but are not limited to, P-selectin, PECAM, CD63 and CD9.

In embodiments of the invention, at least one of EV surface markers is a central nervous system (CNS) cell marker. In additional embodiments, the EV surface marker is specific to a neuron, an astrocyte, an oligodendrocyte or a microglia. In embodiments, the EV surface marker is specific to a neuron. In embodiments, the EV surface marker specific to a neuron is L1CAM, NCAM, NRCAM, CHL1, Glu-R2, neurofascin, DAT1, CD90, CD24 or synaptophysin. In embodiments, the neuron is a dopaminergic neuron, a GABAergic neuron, a cholinergic neuron, a serotonergic neuron or a glutamatergic neuron.

In embodiments, the EV surface marker is specific to an astrocyte. In embodiments, the surface marker specific to an astrocyte is ALDH1L1, GLT-1, GLAST, CD184, CD44, A2B5, CD80 or CD86. In embodiments, the EV surface marker is specific to an oligodendrocyte. In embodiments, the surface marker specific to an oligodendrocyte is 04, PDGFRa, CSPG4, GD3, MOG, or MBP. In embodiments, the EV surface marker is specific to a microglia. In embodiments, the microglia surface marker is Tmem119, CD11bF4/80, CD68, P2RY12, CXC3R1. In embodiments, the EV surface marker is a disease-specific biomarker.

In embodiments, the EV surface marker is specific to a T cell, a B cell, a dendritic cell, an NK cell, a monocyte, a macrophage, a granulocyte, a platelet, an erythrocyte, an endothelial cell, an epithelial cell, a stem cell precursor cell, a mesenchymal stem cell, a leukocyte, a T lymphocyte, or a B lymphocyte. T cells include, e.g., helper T cells, such as the subtypes Th1, Th2, Th9, Th17, Th22, and Tfh; regulatory T cells; killer T cells; γδ TCR+ T cells; and natural killer T cells.

In embodiments, the EV surface marker is specific to a T cell, a helper T cell, a regulatory T cell, a killer T cell, a γδ TCR+ T cell, or a natural killer T cell. In embodiments, the surface marker specific to a T cell is CD3, CD4, CD8 or CD2. In embodiments, the surface marker specific to a helper T cell is CD5, CD6, CD45, CD62L, CD197(CCR7), or a/b TCR. In embodiments, the surface marker specific to a helper T cell subtype Th1 is CD183(CXCR3), CD119 (IFNy Ra), CD195 (CCR5), CD218a(IL-18Ra), LT-BR, or CD336 (TIM-3). In embodiments, the surface marker specific to a helper T cell subtype Th2 is CD194(CCR4), Crth2, CDw198(CCR8), CRTH2, IL33-Ra, or CD365(TIM-1). In embodiments, the surface marker specific to a helper T cell subtype Th17 is CD196(CCR6), CD161, or IL-23R. In embodiments, the surface marker specific to a helper T cell subtype Th22 is CCR10. In embodiments, the surface marker specific to a helper T cell subtype Tfh is CD185(CXCR5), CD84, CD126(IL-6Ra), CD150, CD154, CD252(OX40L), CD278(ICOS), or CD279(PD1). In embodiments, the surface marker specific to a regulatory T cell is CD25, CD39, CD73, CD103, CD152(CTLA-4), GARP, or GITR. In embodiments, the surface marker specific to a killer T cell is CD8. In embodiments, the surface marker specific to a γδ TCR+ T cell is γδ TCR. In embodiments, the surface marker specific to a natural killer T cell is CD56 (NCAM), CD11b, CD11c, CD16, CD32, CD49b, CD57, CD69, CD94, CD122, CD158, CD161 (NK1.1), CD244, CD314, CD319, CD328, CD355, Ly49, Ly108, or Vα24-Jα18 TCR.

In embodiments, the EV surface marker is specific to a B cell. In embodiments, the surface marker specific to the B cell is CD19, CD20, CD5, CD9, CDIIa, CD18, CD25, CD26, CD29, CD31, CD38, CD44, CD45, CD49b, CD49c, CD49d, CD50, CD54, CD58, CD62L, CD73, CD95, CD102, CD119, CD120a, CD120b, CD124, or CD166.

In embodiments, the EV surface marker is specific to a dendritic cell. In embodiments, the surface marker specific to the dendritic cell is CD11c, CD123, CDIa, CD33, CD45, CD49d, CD49e, CD58, CD73, CD120a, CD120b, CD123, or CD271.

In embodiments, the EV surface marker is specific to a NK cell. In embodiments, the surface marker specific to the NK cell is CD56, CDIIa, CD18, CD25, CD26, CD29, CD31, CD38, CD45, CD49b, CD49d, CD49e, CD50, CD58, CD59, CD62L, CD95, CD119, CD120a, CD120b, or CD178.

In embodiments, the EV surface marker is specific to a monocyte or a macrophage. In embodiments, the surface marker specific to the monocyte or macrophage is CD14, CD33, CD4, CD9, CDIIa, CD13, CD15, CD18, CD26, CD29, CD31, CD38, CD44, CD45, CD49a, CD49b, CD49c, CD49e, CD49f, CD50, CD51, CD54, CD58, CD59, CD61, CD62L, CD63, CD95, CD102, CD119, CD120a, CD120b, CD123, CD124, or CD127.

In embodiments, the EV surface marker is specific to a granulocyte. In embodiments, the surface marker specific to the granulocyte is CD66b, CD4, CD9, CDIIa, CD13, CD14, CD15, CD18, CD29, CD31, CD33, CD44, CD45, CD50, CD58, CD59, CD63, CD95, CD119, CD120a, CD120b, CD123, or CD178.

In embodiments, the EV surface marker is specific to a platelet. In embodiments, the surface marker specific to the platelet is CD41, CD61, CD62, CD9, CD29, CD31, CD44, CD49b, CD49f, CD51, CD63, CD102, CD120a, CD120b, or CD140a.

In embodiments, the EV surface marker is specific to an erythrocyte. In embodiments, the surface marker specific to the erythrocyte is CD235a, CD49e, CD58, CD59, CD49e, CD58, or CD235a.

In embodiments, the EV surface marker is specific to an endothelial cell. In embodiments, the surface marker specific to the endothelial cell is CD146. In embodiments, the EV surface marker is specific to an epithelial cell. In embodiments, the surface marker specific to the epithelial cell is CD326. In embodiments, the surface marker specific to the endothelial or epithelial cell is CD9, CD10, CD13, CD26, CD29, CD31, CD34, CD49b, CD49c, CD49d, CD49e, CD49f, CD50, CD51, CD54, CD58, CD61, CD62E, CD62P, CD63, CD71, CD90, CD102, CD104, CD105, CD109, CD119, CD120a, CD120b, CD121a, CD123, CD124, CD133, CD140a, CD140b, CD144, CD146, CD166, or CD178.

In embodiments, the EV surface marker is a cancer antigen. In embodiments, the cancer antigen is 5′-nucleotidase (CD73), B7-H3 (CD276), CA19.9, CA60, cadherin-1 (CD324), CD44v6, ADAM10 (CD156c), basigin (CD147), CD24, CD91, Cripto-1 (TSGF1), E-selectin (CD62e), FLT-3 ligand, A1CAM (CD166), Claudin-3, Claudin-4, EGFR, EGFRvIII, CDCP1 (CD318), CEACAM5 (CD66e), Ephrin receptor A2, Glypican-1, HIST2H2BE, HI5T2H2BF, CD44, Galectin-3-binding-protein, MAGE3/6, Gamma-enolase (NSE), IL-2R, KIT (CD117), KNG2DL2 (ULBP-2), EpCAM (CD326), FasR (CD95), FasL, HER-2, ICAM-1 (CD54), Integrin A6 (CD49f), Integrin B4(CD104), Mucin-4, Prominin-1 (CD133), Wnt-2, Mucin-16, Mucin-18 (CD146), Sialyl Lewis X, Syndecan-1 (CD138), TNFR1 (CD120a), upaR (CD87), L1CAM (CD171), MET, MUC1 (CA15-3), Raph Blood group (CD151), Tspan8, EphB4, CEA, ALCAM (CD166), DCC (netrin 1 receptor), LRIG3, Nectin-4, TNFSF8, YES, Galectin-9, Vimentin, or Cytokeratin.

In embodiments, the EV surface marker is specific to a tumor infiltrating leukocyte. In embodiments, the surface marker specific to a tumor infiltrating leukocyte is LAG-3, TIM-3, PD-1 (CD279), CD44, PD-L1, CTLA-4, or CD28. In embodiments, the EV surface marker is an antigen presenting cell marker. In embodiments, the antigen presenting cell marker is CD80, CD86, or CD83. In embodiments, the surface marker is an immuno-oncology marker. In embodiments, the immune-oncology marker is CD137, CD154, or CD40.

In embodiments, the EV surface marker is specific to a stem cell. In embodiments, the surface marker specific to a stem cell is ABCG2 (CD338), CD9, CD11b, CD20, CD29, CD31, CD34, CD44, CD45, CD49f, CD56, CD73, CD81, CD90, CD95, CD105, CD117, CD118, CD133, CD144, CD146, CD166, CD184, DLK1, STRO-1, TNAP, CD24, SSEA-3, SSEA-4, TRA-1-60, or TRA-1-81. In embodiments, the EV surface marker is specific to a mesenchymal stem cell. In embodiments, the surface marker specific to a mesenchymal stem cell is CD73, CD105, CD90, CD29, CD44, CD166, CD13, CD14.

In embodiments, the EV surface marker is a cell adhesion molecule, an integrin, a classical cadherin, a desmosomal cadherin, a protocadherin, an unconventional cadherin, a claudin, or a selectin. In embodiments, the cell adhesion molecule is ICAM1, ICAM2, ICAM3, ICAM4, ICAM5, VCAM1, PECAM-1, NCAM, or ALCAM. In embodiments, the integrin is VLA-1, VLA-2, VLA-3, VLA-4, VLA-5, VLA-6, LFA-1, MAC-1, CD11c/CD18, CD41/CD61, virtonectin-R, or CD49d. In embodiments, the classical cadherin is CDH1, CHD2, CDH12, or CDH3. In embodiments, the desmosomal cadherin is DSG1, DSG2, DSG3, DSG4, DSC1, DSC2, or DSC3. In embodiments, the unconventional cadherin is CDH4, CDH5, CDH6, CDH7, CDH8, CDH9, CDH10, CDH11, CDH13, CDH15, CDH16, CDH17, CDH18, CDH19, CDH20, CDH21, CDH22, CDH23, CDH24, CDH26, CDH28. In embodiments, the claudin is CDLN1, CDLN2, CDLN3, CDLN4, CDLN5, CDLN6, CDLN7, CDLN8, CDLN9, CDLN10, CDLN11, CDLN12, CDLN13, CDLN14, CDLN15, CDLN16, CDLN17, CDLN18, CDLN19, CDLN20, CDLN21, CDLN22, CDLN23 or CDLN24. In embodiments, the selectin is E-selectin, P-selectin, or L-selectin.

In embodiments, the EV surface marker is specific to a senescent cell. In embodiments, the surface marker specific to the senescent cell is DPP4, CD26, CD57, or CD16.

In embodiments, the EV is an exosome, a micro-vesicle or a large-oncosome.

Samples

In embodiments of the methods of the invention, surface marker displaying agents of interest are isolated from samples using the methods of the invention. In embodiments of the invention, the sample comprises the surface marker displaying agents of interest and unwanted components. In embodiments of the methods of the invention, before contacting the sample with a surface and selectively binding the surface marker displaying agents of interest, the sample, e.g., mammalian fluid, secretion, or excretion, is purified by, for instance, differential centrifugation, ultrafiltration, size-exclusion chromatography, immuno-affinity, precipitation, or a combination thereof. In embodiments, the unwanted components are soluble in the sample and/or the washing fluid. Further unwanted components can include, but are not limited to, surface marker displaying agents that do not have the marker that the capture reagent binds to, the marker that the binding reagent binds to, or both. In embodiments, the unwanted components include surface marker displaying agents that bind to the capture reagent, but not the binding reagent. In the methods of the invention, surface marker displaying agents that bind to the capture reagent, but not the binding reagent, will be eluted following releasing the capture reagent from the surface. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments of the methods of the invention, EVs of interest are isolated from samples using the methods of the invention. In embodiments of the invention, the sample comprises the EVs of interest and unwanted components. In embodiments of the methods of the invention, before contacting the sample with a surface and selectively binding the EV of interest, the sample, e.g., mammalian fluid, secretion, or excretion, is purified by, for instance, differential centrifugation, ultrafiltration, size-exclusion chromatography, immuno-affinity, precipitation, or a combination thereof. In embodiments, the unwanted components are soluble in the sample and/or the washing fluid. Further unwanted components can include, but are not limited to, EVs that do not have the marker that the capture reagent binds to, the marker that the binding reagent binds to, or both. In embodiments, the unwanted components include EVs that bind to the capture reagent, but not the binding reagent. In the methods of the invention, EVs that bind to the capture reagent, but not the binding reagent, will be eluted following releasing the capture reagent from the surface.

In embodiments of the methods of the invention, the sample comprises EVs produced from a cell differentiated from a cell-line, differentiated from an induced pluripotent stem cell, a primary cell, or a combination thereof. Samples further include cell supernatants, such as those from neuronal and astrocyte cultures, which include at least the following: human cortical neurons differentiated from induced pluripotent stem cells (iPSC) and from the HCN-2 cell line, as well as mature astrocytes differentiated from iPSC and primary human astrocytes. In embodiments, samples include supernatants from oligodendrocytes derived from iPSC cells, which are commercially available, and from cell lines such as HOG or M03.13 which can be differentiated to mature oligodendrocytes using established protocols. Samples further include iPSC derived microglia, which are commercially available, as well as primary microglia which can be expanded in culture. Non-limiting examples of cell lines include MOLT-4 (differentiated or undifferentiated), Jurkat, HL60 (differentiated or undifferentiated), U-937 (differentiated or undifferentiated), HDLM-2, THP-1 (differentiated or undifferentiated), GA10, Ramos, HUVEC, PANC-1, Expi293, HaCat, HCT-15, H-2228, peripheral blood mononuclear cells (PBMCs), KU-812, MC-04, HT-1376, TT, HCT-1116, MCF-7, Calu-3, and the like.

In embodiments, the samples comprise EVs produced from a T cell, a B cell, a dendritic cell, an NK cell, a monocyte, a macrophage, a granulocyte, a platelet, an erythrocyte, an endothelial cell, an epithelial cell, a stem cell precursor cell, a mesenchymal stem cell, a leukocyte, or a senescent cell. T cells include, e.g., helper T cells, such as the subtypes Th1, Th2, Th9, Th17, Th22, and Tfh; regulatory T cells; killer T cells; γδ TCR+ T cells; and natural killer T cells.

In embodiments of the invention, the sample is a mammalian fluid, secretion, or excretion. In embodiments, the sample is a purified mammalian fluid, secretion, or excretion.

In embodiments, the mammalian fluid, secretion, or excretion is whole blood, plasma, serum, sputum, lachrymal fluid, lymphatic fluid, synovial fluid, pleural effusion, urine, sweat, cerebrospinal fluid, ascites, milk, stool, bronchial lavage, saliva, amniotic fluid, nasal secretions, vaginal secretions, a surface biopsy, sperm, semen/seminal fluid, wound secretions and excretions. In embodiments, the sample is cerebrospinal fluid.

In embodiments, the sample comprises purified EVs. Methods of purification include, but are not limited to, precipitation, ultracentrifugation, size exclusion chromatography, ultrafiltration, or affinity purification. In embodiments, the affinity purification may be performed with magnetic or non-magnetic beads.

Biological samples that may be analyzed include, but are not limited to, physiological samples and/or samples containing suspensions of cells, such as mucosal swabs, tissue aspirates, tissue homogenates, cell cultures, and cell culture supernatant, including cultures of eukaryotic and prokaryotic cells. In embodiments, cells are removed, before contacting the surface with EVs, by, for instance centrifugation or filtration.

In embodiments, different cells are identified and distinguished from each other, based on the EVs detected using the present methods. For example, the present methods may be used to distinguish between differentiated and undifferentiated cells, or between diseased and normal (healthy) cells, based on the EVs secreted by each type of cell. The present methods may also be used to determine the growth stage or stimulated state of a cell or cell population. For example, the present methods may be used to compare multiple growth or stimulation conditions on a single cell line. Advantageously, the present methods facilitate comparison of EV secretion in multiple cell lines and reduce potentially tedious sample preparation.

In embodiments, the relative abundance of EVs in a sample can be measured by using a plurality of different capture reagents to capture different EVs expressing different markers, then detecting each type of captured EVs with the same detection reagent to a common marker on the different EVs. In embodiments, the relative abundance of EVs in a sample can be measured by using the same capture reagent to capture different EVs expressing a common marker, then using a plurality of different detection reagents to determine the different markers expressed by the EVs.

Surface Comprising Capture Reagent and Anchoring Reagent

In embodiments of the invention, a sample comprising a surface marker displaying agent of interest is contacted with a surface, wherein the surface comprises a releasably bound capture reagent and an anchoring reagent.

In embodiments of the invention, a sample comprising an EV of interest is contacted with a surface, wherein the surface comprises a releasably bound capture reagent and an anchoring reagent. The term “contacting” has its ordinary meaning to one of skill in the art. Methods of contacting samples, e.g., liquids, solids, gels, etc., are known to those of ordinary skill in the art.

In embodiments of the methods of the invention, the capture reagent is releasably bound to the surface by a labile linker. In embodiments, the labile linker is a heat-labile, a photolabile, or a chemically labile linker. In additional embodiments, the labile linker is an oligonucleotide that is complementary to an oligonucleotide bound to the surface or is an oligonucleotide comprising a restriction site cleavable by a restriction endonuclease. In embodiments, the labile linker is a small molecule that binds to a protein on the surface. In embodiments, the capture reagent is biotinylated, and the surface is coated with streptavidin. The surface can be, for example, an MSD plate electrode or a particle. In some embodiments, the surface is directly coated with the capture reagent.

In embodiments, the capture reagent is an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer. In embodiments of the methods of the invention, the capture reagent and the binding reagent are antibodies, or epitope binding portions thereof, capable of specifically binding a target molecule in or on the surface of the EV of interest.

In embodiments, the EV surface marker to which the capture reagent binds is common to EVs. Such surface markers include, but are not limited e.g., tetraspanins, such as CD9, CD37, CD63, CD81, CD82. In embodiments, the EV surface marker to which the capture reagent binds is specific to a central nervous system (CNS) EV. In embodiments, the EV surface marker to which the capture reagent binds is specific to a neuron EV, an astrocyte EV, an oligodendrocyte EV or a microglia EV.

In embodiments, the EV surface marker to which the capture reagent binds is specific to a neuron EV. In embodiments, the neuron-specific EV surface marker to which the capture reagent binds is L1CAM, NCAM, NRCAM, CHL1, Glu-R2, neurofascin, DAT1, CD90, CD24 or synaptophysin. In embodiments, the neuron that has an EV surface marker to which the capture reagent binds is a dopaminergic neuron, a GABAergic neuron, a cholinergic neuron, a serotonergic neuron or a glutamatergic neuron.

In embodiments, the EV surface marker to which the capture reagent binds is specific to an astrocyte EV. In embodiments, the astrocyte-specific EV surface marker to which the capture reagent binds is ALDH1L1, GLT-1, GLAST, CD184, CD44, A2B5, CD80 or CD86.

In embodiments, the EV surface marker to which the capture reagent binds is specific to an oligodendrocyte EV. In embodiments, the oligodendrocyte-specific EV surface marker to which the capture reagent binds is 04, PDGFRa, CSPG4 (NG2, MCSP), GD3, MOG, or MBP.

In embodiments, the EV surface marker to which the capture reagent binds is specific to a microglia EV. In embodiments, the microglia-specific EV surface marker to which the capture reagent binds is Tmem119, CD11bF4/80, CD68, P2RY12, or CXC3R1.

In embodiments of the invention, the capture reagent is an antibody to a disease-specific target molecule in or on the surface of the EV. In embodiments, the EV surface marker to which the binding reagent binds is a cancer antigen. In embodiments, the cancer antigen to which the capture reagent and/or the binding reagent binds is CEA, CA19.9, CA50, CA125, CA15.3, mesothelin, cytokeratin-8, E-cadherin, EGFR, EpCAM, EphA2, NCAM, P-cadherin, cMET, Flt-3L, TNFR-2, cKit, ErbB2, or ANXA1.

In embodiments of the methods of the invention, the surface comprises an anchoring reagent. In the methods of the invention, the anchoring reagent is attached to the surface to allow linker oligonucleotide binding and/or amplicon binding in order to provide an additional indirect attachment point at the surface for the EV of interest. In embodiments, the anchoring reagent includes an oligonucleotide sequence, aptamer, aptamer ligand, antibody, antigen, ligand, receptor, hapten, epitope, or a mimetope; and optionally, the anchoring region can include an aptamer and the anchoring reagent can include an aptamer ligand/target molecule. The anchoring region, in embodiments, comprises a nucleic acid sequence and/or a DNA- or RNA-binding protein. The anchoring reagent comprises, in embodiments, oligonucleotide sequence and the anchoring reagent can include a complementary oligonucleotide sequence. The anchoring reagent, for example, can be a single stranded oligonucleotide sequence or a double stranded oligonucleotide sequence. In embodiments of the invention, the anchoring reagent features, etc., are disclosed in International Appl. No. PCT/US2015/030925, published as WO 2015/175856, which is incorporated by reference in its entirety.

In additional embodiments, the amplicon is bound to the anchoring reagent at a position within 10 μm, 5 μm, or 100 nm of the location of the complex comprising the EV of interest on the surface.

Suitable surfaces for use in the methods of the present invention are known in the art, including conventional surfaces from the art of binding assays. Suitable surfaces are disclosed, for example, in International Appl. No. PCT/US2015/030925, published as WO 2015/175856. Surfaces may be made from a variety of different materials including polymers (e.g., polystyrene and polypropylene), ceramics, glass, composite materials (e.g., carbon-polymer composites such as carbon-based inks). Suitable surfaces include the surfaces of macroscopic objects such as an interior surface of an assay container (e.g., test tubes, cuvettes, flow cells, FACS cell sorter, cartridges, wells in a multi-well plate, etc.), slides, assay chips (such as those used in gene or protein chip measurements), pins or probes, beads, filtration media, lateral flow media (for example, filtration membranes used in lateral flow test strips), etc.

Suitable surfaces also include particles (including but not limited to colloids or beads) commonly used in other types of particle-based assays e.g., magnetic, polypropylene, and latex particles, hydrogels, e.g. agarose, materials typically used in solid-phase synthesis e.g., polystyrene and polyacrylamide particles, and materials typically used in chromatographic applications e.g., silica, alumina, polyacrylamide, polystyrene. The materials may also be a fiber such as a carbon fibril. Microparticles may be inanimate or alternatively, may include animate biological entities such as cells, viruses, bacterium and the like. A particle used in the present method may be comprised of any material suitable for attachment to one or more capture or anchoring reagents, and that may be collected via, e.g., centrifugation, gravity, filtration or magnetic collection. A wide variety of different types of particles that may be attached to capture or anchoring reagents are sold commercially for use in binding assays. These include non-magnetic particles as well as particles comprising magnetizable materials which allow the particles to be collected with a magnetic field. In one embodiment, the particles are comprised of a conductive and/or semiconductive material, e.g., colloidal gold particles. The microparticles may have a wide variety of sizes and shapes. By way of example and not limitation, microparticles may be between 5 nanometers and 100 micrometers. Preferably microparticles have sizes between 20 nm and 10 micrometers. The particles may be spherical, oblong, rod-like, etc., or they may be irregular in shape.

The particles used in the present method may be coded to allow for the identification of specific particles or subpopulations of particles in a mixture of particles. The use of such coded particles has been used to enable multiplexing of assays employing particles as solid phase supports for binding assays. In one approach, particles are manufactured to include one or more fluorescent dyes and specific populations of particles are identified based on the intensity and/or relative intensity of fluorescence emissions at one or more wave lengths. This approach has been used in the Luminex xMAP systems (see, e.g., U.S. Pat. No. 6,939,720) and the Becton Dickinson Cytometric Bead Array systems. Alternatively, particles may be coded through differences in other physical properties such as size, shape, imbedded optical patterns and the like. One or more particles provided in a mixture or set of particles may be coded to be distinguishable from other particles in the mixture by virtue of particle optical properties, size, shape, imbedded optical patterns and the like.

In a specific embodiment, the methods of the invention can be used in a multiplexed format by binding a plurality of different analytes to a plurality of capture reagents for those analytes, the capture analytes being immobilized on coded bead, such that the coding identifies the capture reagent (and analyte target) for a specific bead. The method may further comprise counting the number of beads that have a bound analyte (using the detection approaches described herein).

Alternatively or additionally, the capture reagents can be bound, directly or indirectly, to different discrete binding domains on one or more solid phases, e.g., as in a binding array wherein the binding domains are individual array elements, or in a set of beads wherein the binding domains are the individual beads, such that discrete assay signals are generated on and measured from each binding domain. If capture reagents for different analytes are immobilized in different binding domains, the different analytes bound to those domains can be measured independently. In one example of such an embodiment, the binding domains are prepared by immobilizing, on one or more surfaces, discrete domains of capture reagents that bind analytes of interest. Optionally, the surface(s) may define, in part, one or more boundaries of a container (e.g., a flow cell, well, cuvette, etc.) which holds the sample or through which the sample is passed. In a preferred embodiment, individual binding domains are formed on electrodes for use in electrochemical or electrochemiluminescence assays. Multiplexed measurement of analytes on a surface comprising a plurality of binding domains using electrochemiluminescence has been used in the Meso Scale Diagnostics, LLC, MULTI-ARRAY® and SECTOR® Imager line of products (see, e.g., U.S. Pat. Nos. 10,201,812, 7,842,246 and 6,977,722, the disclosures of which are incorporated herein by reference in their entireties).

Still further, the capture reagents can be bound, directly or indirectly, to an electrode surface, which optionally includes different discrete binding domains, as described above. The electrode surface can be a component of a multi-well plate and/or a flow cell. Electrodes can comprise a conductive material, e.g., a metal such as gold, silver, platinum, nickel, steel, iridium, copper, aluminum, a conductive allow, or the like. They may also include oxide coated metals, e.g., aluminum oxide coated aluminum. The electrode can include a working and counter electrodes which can be made of the same or different materials, e.g., a metal counter electrode and carbon working electrode. In one specific embodiment, electrodes comprise carbon-based materials such as carbon, carbon black, graphitic carbon, carbon nanotubes, carbon fibrils, graphite, graphene, carbon fibers and mixtures thereof. In one embodiment, the electrodes comprise elemental carbon, e.g., graphitic, carbon black, carbon nanotubes, etc. Advantageously, they may include conducting carbon-polymer composites, conducting particles dispersed in a matrix (e.g. carbon inks, carbon pastes, metal inks, graphene inks), and/or conducting polymers. One specific embodiment of the invention is an assay module, preferably a multi-well plate, having electrodes (e.g., working and/or counter electrodes) that comprise carbon, e.g., carbon layers, and/or screen-printed layers of carbon inks.

In embodiments, the capture reagent is attached to the surface via a pair of short complementary oligonucleotides (one attached to the surface, the other attached to the capture reagent) that form stable duplexes in common biological buffers but can be denatured in a low salt buffer, and modestly elevated temperature is used to allow the capture reagent, e.g., antibody to be released. In embodiments, a restriction site in the complementary oligonucleotides that is cleaved by a restriction endonuclease is used. This has the advantage of being completely orthogonal to the denaturation that will be used, in embodiments, to purposely elute the stapled EVs, though a second restriction enzyme can also be used to elute the stapled EVs. Stapling sequence, diluents, and procedure are optimized to maximize retention of stapled EVs and minimize retention of non-stapled EVs. In embodiments, the captured EVs are co-labeled with STAG-labeled detection antibodies, and the ECL signal is compared with the ECL signal generated with and without elution, or with specific stapling and irrelevant stapling.

In embodiments of the invention, the capture reagent binds to a first surface marker on the EV and the binding reagent binds to a second surface marker on the EV.

Binding Reagents and Stapling Step

In embodiments of the invention, following binding of the surface marker displaying agent of interest with a capture reagent that is releasably bound to the surface, at least one binding reagent is contacted with the surface marker displaying agent. In embodiments, a complex is thus formed on the surface comprising the capture reagent, the surface marker displaying agent and a binding reagent. In embodiments, the binding reagent comprises a binding site for a surface marker on the surface marker displaying agent. In embodiments, the binding reagent surface marker is distinct from the surface marker to which the capture reagent is bound. In embodiments, the capture reagent binds to a surface marker common to surface marker displaying agents, and the binding reagent binds to a surface marker displaying agent surface marker specific to a type of surface marker displaying agent, e.g., a cancer cell in a sample of blood cells. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments of the invention, following binding of the EV of interest with a capture reagent that is releasably bound to the surface, at least one binding reagent is contacted with the EV. In embodiments, a complex is thus formed on the surface comprising the capture reagent, the EV and a binding reagent. In embodiments, the binding reagent comprises a binding site for a surface marker on the EV. In embodiments, the binding reagent surface marker is distinct from the surface marker to which the capture reagent is bound. In embodiments, the capture reagent binds to a surface marker common to EVs, and the binding reagent binds to an EV surface marker specific to a cell, tissue, or organ specific marker such as a CNS marker.

The binding reagent, in embodiments, comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer. In embodiments, the binding reagent comprises an antibody or an antigen/epitope-binding portion thereof.

In embodiments, the EV surface marker to which the binding reagent binds is common to EVs. Such surface markers include, but are not limited e.g., tetraspanins, such as CD9, CD37, CD63, CD81, CD82. In embodiments, the EV surface marker to which the binding reagent binds is specific to a CNS EV. In embodiments, the EV surface marker to which the binding reagent binds is specific to a neuron EV, an astrocyte EV, an oligodendrocyte EV or a microglia EV.

In embodiments, the EV surface marker to which the binding reagent binds is specific to a neuron EV. In embodiments, the EV surface marker to which the binding reagent binds is L1CAM, NCAM, NRCAM, CRL1, Glu-R2, neurofascin, DAT1, CD90, CD24 or synaptophysin. In embodiments, the neuron EV surface marker to which the binding reagent binds is from a dopaminergic neuron, a GABAergic neuron, a cholinergic neuron, a serotonergic neuron or a glutamatergic neuron.

In embodiments, the EV surface marker to which the binding reagent binds is specific to an astrocyte EV. In embodiments, the EV surface marker to which the binding reagent binds is ALDH1L1, GLT-1, GLAST, CD184, CD44, A2B5, CD80 or CD86.

In embodiments, the EV surface marker to which the binding reagent binds is specific to an oligodendrocyte EV. In embodiments, the EV surface marker to which the binding reagent binds is 04, PDGFRa, CSPG4 (NG2, MCSP), GD3, MOG, or MBP.

In embodiments, the EV surface marker to which the binding reagent binds is specific to a microglia EV. In embodiments, the EV surface marker to which the binding reagent binds is Tmem119, CD11bF4/80, CD68, P2RY12, CXC3R1.

In embodiments of the invention, at least one of the first or second binding reagents are antibodies to a disease-specific target molecule in or on the surface of the EV. In embodiments, the EV surface marker to which the binding reagent binds is specific to an Alzheimer's biomarker.

In embodiments, in addition to a binding site for an EV surface marker, the binding reagent comprises an oligonucleotide that allows the EV of interest to be indirectly attached or linked to the surface. In embodiments, the binding reagent oligonucleotide is a tag oligonucleotide that contains a sequence that is complementary to an anchoring oligonucleotide that is attached to the surface. Thus when the binding reagent oligonucleotide is hybridized to the anchoring oligonucleotide the EV of interest is indirectly bound to the surface by these interactions

In embodiments of the methods of the invention the binding reagent oligonucleotide comprises a region complementary to the anchoring nucleotide of about 15 to 35 oligonucleotides. In embodiments, the region is 20-30 oligonucleotides. In additional embodiments the capture reagent is also releasably attached to the surface via a pair of hybridized oligonucleotides with one oligonucleotide attached to the capture reagent and one oligonucleotide attached to the surface. In additional embodiments, the complementary portions of the hybridized oligonucleotides attaching the capture reagent to the surface are optimized to be releasable at a lower temperature or less strict conditions than the hybridized regions of the binding reagent oligonucleotide and the anchoring oligonucleotide.

In embodiments, the binding reagent oligonucleotide is a tag oligonucleotide that contains a sequence that is complementary to a linker oligonucleotide. In embodiments, the linker oligonucleotide further contains a sequence that is complementary to an anchoring oligonucleotide that is attached to the surface. Thus, when a linker oligonucleotide is hybridized to the tag oligonucleotide and to an anchoring oligonucleotide, the EV of interest is indirectly bound to the surface by these interactions.

In embodiments of the methods of the invention the linker oligonucleotide comprises a first region complementary to the tag nucleotide of about 15 to 35 oligonucleotides and a second region complementary to the anchoring nucleotide of about 15 to 35 oligonucleotides. In embodiments, the first and second region are each 20-30 oligonucleotides. In additional embodiments the capture reagent is also releasably attached to the surface via a pair of hybridized oligonucleotides with one oligonucleotide attached to the capture reagent and one oligonucleotide attached to the surface. In additional embodiments the complementary portions of the hybridized oligonucleotides attaching the capture reagent to the surface are optimized to be releasable at a lower temperature or less strict conditions than the hybridized regions of the linker oligonucleotide and the binding reagent and the hybridized regions of the linker oligonucleotide and the anchoring oligonucleotide.

In additional embodiments, the binding reagent comprises a primer oligonucleotide that contains a sequence that is complementary to an oligonucleotide template, such as a circular oligonucleotide. The primer is used to form an amplicon that comprises a sequence complementary to an anchoring oligonucleotide. Any suitable amplification technique can be used to generate the extended sequence (or amplicon), including but not limited to, PCR (Polymerase Chain Reaction), LCR (Ligase Chain Reaction), and isothermal amplification methods, e.g., helicase-dependent amplification, rolling circle amplification (RCA), 3SR (Self-Sustained Synthetic Reaction), transcription mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), signal mediated amplification of RNA technology, strand displacement amplification (SDA), loop-mediated isothermal amplification of DNA (LAMP), isothermal multiple displacement amplification, single primer isothermal amplification, and circular helicase-dependent amplification. In embodiments, the amplification technique is proximity ligation amplification (PLA) using RCA, which is known in the art, and disclosed in International Appl. No. PCT/US2015/030925, published as WO 2015/175856, which is incorporated by reference in its entirety.

In additional embodiments, the amplicon further comprises one or more detection sequences and the measuring step further comprises contacting the extended sequence with a plurality of labeled probes complementary to the one or more detection sequences.

In further embodiments, the amplicon remains localized on the surface following the amplification. In further embodiments of the methods of the invention, the amplicon remains bound to the surface after the amplification.

In a preferred embodiment, RCA is used to make the amplicon because it has significant advantages in terms of sensitivity, multiplexing, dynamic range and scalability. Techniques for RCA are known in the art (see, e.g., Baner et al, Nucleic Acids Research, 26:5073 5078, 1998; Lizardi et al., Nature Genetics 19:226, 1998; Schweitzer et al. Proc. Natl. Acad. Sci. USA 97:10113 119, 2000; Faruqi et al., BMC Genomics 2:4, 2000; Nallur et al., Nucl. Acids Res. 29:e118, 2001; Dean et al. Genome Res. 11:1095 1099, 2001; Schweitzer et al., Nature Biotech. 20:359 365, 2002; U.S. Pat. Nos. 6,054,274, 6,291,187, 6,323,009, 6,344,329 and 6,368,801). Several different variants of RCA are known, including linear RCA (LRCA) and exponential RCA (ERCA). RCA generates many thousands of copies of a circular template, with the chain of copies attached to the original target DNA, allowing for spatial resolution of target and rapid amplification of the signal. RCA facilitates (i) detection of single target molecules; (ii) amplification of signals from proteins as well as DNA and RNA; (iii) identifying the location of molecules that have been amplified on a solid surface; (iv) measurement of many different targets simultaneously; and (v) analysis of one or more targets in solution or solid phase. The spatial localization of RCA products with the detection complex is especially advantageous when conducting multiplexed binding assays in an array or particle based format.

Releasing Capture Reagent and Eluting Unwanted Components

In embodiments of the invention, after the surface marker displaying agent of interest is indirectly attached to the surface by at least two attachment points, e.g., by the capture reagent and the binding reagent/anchoring reagent complex, the capture reagent is released from the surface and unwanted components are eluted from the surface using, e.g., a washing solution.

In embodiments of the invention, after the EV of interest is indirectly attached to the surface by at least two attachment points, e.g., by the capture reagent and the binding reagent/anchoring reagent complex, the capture reagent is released from the surface and unwanted components are eluted from the surface using, e.g., a washing solution. The unwanted components include, but are not limited to, components soluble in the washing solution, or components that do not have the surface marker that the binding reagent binds to.

The specific release of the capture reagent depends on how the capture reagent is releasably bound to the surface. For example, if the capture reagent is releasably bound to the surface by complementary oligonucleotides, the releasing comprises denaturation, whereas if the capture reagent is bound to the surface by an oligonucleotide comprising a restriction site, releasing comprises cleaving by a restriction endonuclease.

In embodiment of the methods of the invention, the attachment of the EV to the surface by the binding reagent/anchoring reagent complex is stable during the release of the capture reagent from the surface. For example, the hybridized anchoring oligonucleotide and amplicon is stable during the release of the capture reagent from the surface.

In embodiments of the methods of the invention, the hybridized linker oligonucleotide and tag oligonucleotide and the hybridized linker oligonucleotide and anchoring oligonucleotide are stable during the releasing of the capture reagent from the surface.

Releasing and Eluting Surface Marker Displaying Agents of Interest

In embodiments of the methods of the invention, following release of the capture reagent from the surface and elution of unwanted components of the sample from the surface, the surface marker displaying agent of interest is released from the surface. In embodiments, the surface marker displaying agent is released from the surface and further analyzed. In embodiments, the surface marker displaying agents are eluted with the capture antibody still bound to the surface marker displaying agent surface marker(s). The eluted surface marker displaying agents, for example, can then be assayed with the bound capture antibody, or a low-pH elution can be performed to remove the antibodies.

In embodiments of the methods of the invention, following release of the capture reagent from the surface and elution of unwanted components of the sample from the surface, the EV of interest is released from the surface. In embodiments, the EV is released from the surface and further analyzed. In embodiments, the EVs are eluted with the capture antibody still bound to the EV surface marker(s). The eluted EVs, for example, can then be assayed with the bound capture antibody, or a low-pH elution can be performed to remove the antibodies.

Labeled capture antibodies can be coupled to the solid phase using cleavable linkers or multiplex assay linkers. In embodiments, after releasing the antibodies from the solid phase to elute the surface marker displaying agents, e.g., EVs, the surface marker displaying agents, e.g., EVs, are captured with a second marker on an assay plate. In such instances, the surface marker displaying agents, e.g., EVs, already include the labeled capture antibodies, and thus no extra detection step is necessary. Elimination of the extra detection step is advantageous when the desired capture antibody has a high off-rate, which would create challenges in a typical two-step assay.

In embodiments, the surface marker displaying agent, e.g., EV, of interest is released from the surface by denaturing the tag oligonucleotide and the linker oligonucleotide, or the linker oligonucleotide and the anchoring oligonucleotide, or both. In additional embodiments, the surface marker displaying agent, e.g., EV, of interest is released by denaturing the anchoring oligonucleotide and amplicon. In additional embodiments, the anchoring oligonucleotide is detached from the surface, or cleaved in the case that the anchoring oligonucleotide contains a restriction site. Methods of denaturing oligonucleotides and additional methods of releasing bound components are well known to those of skill in the art.

Release, as used herein, refers to delocalization of a previously collected material. Materials that are held at a localized position through chemical bonds or through specific or non-specific binding interactions may be allowed to delocalize by breaking the bond or interaction so that the materials may diffuse or mix into the surrounding media. There are many well-established cleavable chemical linkers that may be used that provide a covalent bond that may be cleaved without requiring harsh conditions. For example, disulfide containing linkers may be cleaved using thiols or other reducing agents, cis-diol containing linkers may be cleaved using periodate, metal-ligand interactions (such as nickel-histidine) may be cleaved by changing pH or introducing competing ligands. Similarly, there are many well-established reversible binding pairs that may be employed (including those that have been identified in the art of affinity chromatography). By way of example, the binding of many antibody-ligand pairs can be reversed through changes in pH, addition of protein denaturants or chaotropic agents, addition of competing ligands, etc. Other suitable reversible binding pairs include complementary nucleic acid sequences, the hybridization of which may be reversed under a variety of conditions including changing pH, decreasing salt concentration, increasing temperature above the melting temperature for the pair and/or adding nucleic acid denaturants (such as formamide).

Release also includes physical delocalization of materials by, for example, mixing, shaking, vortexing, convective fluid flow, mixing by application of magnetic, electrical or optical forces and the like. Where microparticles or materials bound to microparticles have been collected, such physical methods may be used to resuspend the particles in a surrounding matrix. Release may simply be the reverse of a previous collection step (e.g., by any of the mechanisms described above) or collection and release could proceed by two different mechanisms. In one such example, collection of materials (such as an analyte or a complex comprising an analyte) bound to a particle can be achieved by physical collection of the particle. The materials are then released by cleaving a bond or reversing a binding reaction holding the material on the particle. In a second such example, materials (such as an analyte of a complex comprising an analyte are collected on a surface through a binding interaction with a binding reagent that is linked to the surface. The material is then released by breaking a bond or a second binding interaction linking the binding reagent to the surface.

Collection followed by release may be used to concentrate and/or purify analytes in a sample. By collecting in a first volume and releasing into a second smaller volume, an analyte in a sample can be concentrated. Through concentration, it is often possible to significantly improve the sensitivity of a subsequent measurement step. By collecting from a sample and removing some or all of the uncollected sample, potential assay interferents in the sample may be reduced or eliminated. Optionally, removal of the unbound sample may include washing a collected material with and releasing the collected material into defined liquid reagents (e.g., assay or wash buffers) so as to provide a uniform matrix for subsequent assay steps.

As illustrated in FIG. 3(a) of US 2010/0261292, which is incorporated herein by reference in its entirety, the method includes contacting a sample comprising a target analyte (herein, an EV) with a particle linked to a first binding reagent (herein, a capture reagent) that binds the target analyte, wherein the first binding reagent is linked to a first targeting agent and the particle is linked to a second targeting agent, and the first binding reagent and the particle are linked via a binding reaction between the first and second targeting agents to form a complex comprising said target analyte bound to said first binding reagent. The complex is then collected and unbound components in the sample are separated from the complex.

Alternative Stapling Methods

In embodiments, the present disclosure provides methods of isolating a surface marker displaying agent using multiple (e.g., three) markers for the same surface marker displaying agent. In embodiments, a method of isolating a surface marker displaying agent of interest in a sample comprises: contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences; (ii) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent, and binding the anchoring reagent to the second binding reagent, wherein the anchoring reagent is bound to the second binding reagent by an adaptor oligonucleotide, wherein the adaptor oligonucleotide comprises (1) a nucleotide sequence complementary to a nucleotide sequence of the anchoring reagent, and (2) a nucleotide sequence complementary to a nucleotide sequence of the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; and releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments, the present disclosure provides methods of isolating an EV using multiple (e.g., three) markers for the same EV. In embodiments, a method of isolating an EV of interest in a sample comprises: contacting the sample with a surface and selectively binding the EV of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences; (ii) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent, and binding the anchoring reagent to the second binding reagent, wherein the anchoring reagent is bound to the second binding reagent by an adaptor oligonucleotide, wherein the adaptor oligonucleotide comprises (1) a nucleotide sequence complementary to a nucleotide sequence of the anchoring reagent, and (2) a nucleotide sequence complementary to a nucleotide sequence of the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; and releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

In embodiments, the capture reagent is releasably bound to the surface by an oligonucleotide comprising a first cleavage site, e.g., restriction site, and wherein the adaptor oligonucleotide comprises a second cleavage site, e.g., restriction site. In embodiments, the surface is a bead or a planar substrate having multiple binding sites.

In embodiments, the sample comprises at least two EVs of interest, and the surface comprises at least a first bead and a second bead, wherein a first capture reagent releasably bound to the first bead binds to a first EV and a second capture reagent releasably bound to the second bead binds to a second EV.

In embodiments, the sample comprises at least two EVs of interest and the surface comprises at least a first region and a second region, wherein a first capture reagent releasably bound to the first region binds to a first EV and a second capture reagent releasably bound to the second region binds to a second EV.

In embodiments, a method of isolating a surface marker displaying agent, e.g., an EV, of interest from a sample using multiple (e.g., three) markers and a single solid phase is illustrated in FIG. 32 and includes:

1. Contacting the sample containing the surface marker displaying agent, e.g., EV, of interest with: a capture reagent releasably bound to a solid phase (e.g., a bead or a planar surface having multiple binding sites), wherein the surface further comprises an anchoring reagent (e.g., an anchoring oligonucleotide); and first and second binding reagents (e.g., detection antibodies).

In embodiments, the capture reagent is bound to the solid phase via an oligonucleotide sequence comprising a first cleavage site. In embodiments, the first and second binding reagents comprise complementary nucleotide sequences. In embodiments, the adaptor oligonucleotide comprises a complementary nucleotide sequence to a nucleotide sequence of the anchoring reagent, and a complementary nucleotide sequence to a nucleotide sequence of the second binding reagent. In embodiments, the cleavage site is a restriction site. In embodiments, the cleavage site is a labile linker. In embodiments, the labile linker is a heat-labile, photolabile, or chemically-labile linker. In embodiments, the labile linker is an oligonucleotide that is complementary to an oligonucleotide bound to the surface or is an oligonucleotide comprising a restriction site cleavable by a restriction endonuclease. In embodiments, the labile linker is a small molecule that binds to a protein on the surface.

In embodiments, the first binding reagent includes a first oligonucleotide sequence that includes a first barcode sequence and a complementary nucleotide sequence to the second binding reagent. In embodiments, the second binding reagent includes a second oligonucleotide sequence that includes a second barcode sequence, a complementary nucleotide sequence to the first binding reagent, and a complementary nucleotide sequence to an adaptor oligonucleotide. In embodiments, the capture reagent is bound to the solid phase via a third oligonucleotide sequence that includes a third barcode sequence and a first cleavage site. In embodiments, the first cleavage site is a first restriction site. In embodiments, the first cleavage site is a labile linker.

A “barcode sequence” or “barcode oligonucleotide sequence,” as used herein, refers to a short nucleotide (typically between about 5 and about 40 nucleotides in length) that allows a corresponding nucleotide or molecule to be identified. In embodiments, the corresponding nucleotide or molecule is attached to the barcode sequence. In embodiments, the molecule is a peptide, a protein, a protein complex, an antibody, or a vesicle. In embodiments, the barcode sequence is a unique nucleotide identifiable by sequencing. In embodiments, the barcode sequence is hybridizable to a complementary detectable probe. In such embodiments, the complementary detectable probe hybridizes to the barcode sequence, allowing the corresponding nucleotide or molecule to be detected. Barcode technologies are described in, e.g., Winzeler et al., Science 285:901-906 (1999), Eason et al., Proc Natl Acad Sci 101(30):11046-11051 (2004), and Fredriksson et al., Nature Methods 4(4):327-329 (2007), each of which is herein incorporated by reference in its entirety.

2. Adding an adaptor oligonucleotide to the complex. In embodiments, the adaptor oligonucleotide includes a nucleotide sequence complementary to the anchoring oligonucleotide, a second cleavage site (for example, a second restriction site), a fourth barcode sequence, and a complementary nucleotide sequence to the second binding reagent. In some embodiments, the adaptor oligonucleotide hybridizes with the anchoring oligonucleotide and second binding reagent, thereby forming a complex on the solid phase comprising: the capture reagent, EV, first and second binding reagents, and the adaptor oligonucleotide.

In embodiments, the second oligonucleotide sequence does not include a barcode sequence.

3. Eluting unwanted components (e.g., unbound surface marker displaying agent, e.g., EVs or binding reagents) from the sample.

4. Adding polymerase, ligase, or both to the sample to ligate together the second, third, and fourth oligonucleotides at the ligation site, thereby forming a “staple.”

In embodiments, the complementary nucleotide sequences of the second, third, and fourth oligonucleotides are ligated together with a ligase, and polymerase is added to remove any gaps in the sequence. In embodiments, the complementary nucleotide sequences of the second, third, and fourth oligonucleotides are ligated together using additional short oligonucleotides that are complementary to any gaps in the sequence.

5. Releasing the capture binding reagent from the solid phase by cleaving at the first cleavage site and eluting unwanted components (e.g., unbound surface marker displaying agent, e.g., EVs) from the sample.

6. Isolating the surface marker displaying agent, e.g., EV, by cleaving at the second cleavage site, or by eluting the adaptor oligonucleotide from the solid phase, to release the surface marker displaying agent, e.g., EV, of interest.

In embodiments, visualization or quantification of the surface marker displaying agents, e.g., EVs, can be performed using detectably labeled oligonucleotides complementary to the first, second, third, or fourth barcode sequences, prior to releasing the surface marker displaying agents, e.g., EVs, from the solid phase. In embodiments, the capture reagent, the first binding reagent, and/or the second binding reagent can be detected using a detectable probe as described herein, for example, a fluorescent or electrochemiluminescent probe. In embodiments, surface marker displaying agents, e.g., EVs, can be fixed and permeabilized for in situ immunoassays or FISH, prior to releasing the surface marker displaying agents, e.g., EVs, from the solid phase.

In embodiments, two or more different populations of surface marker displaying agents, e.g., EVs, of interest (i.e., different surface marker displaying agents, e.g., EVs) can be isolated. In embodiments, two or more different surface marker displaying agents, e.g., EVs, of interest are immobilized on two different solid phases (e.g., different sets of beads or a planar substrate having multiple binding sites). In embodiments, a single sample is mixed with all of the solid phases in a single reaction capturing different populations of surface marker displaying agents, e.g., EVs, on each solid phase. In embodiments, two or more sets of capture and binding reagents (with each set having one capture and two binding reagents per population of surface marker displaying agent, e.g., EV) are added to the reaction to capture different surface marker displaying agents, e.g., EVs, on different solid phases. The different solid phases may be separated by physical properties (e.g., magnetism, size, or color), or the different surface marker displaying agents, e.g., EVs, may be eluted together. In embodiments, the different EVs are distinguished using detectably labeled oligonucleotides as described herein.

In embodiments, the method includes isolating two different surface marker displaying agents, e.g., EVs, of interest (i.e., first and second surface marker displaying agents, e.g., EVs) from the sample, wherein the two different surface marker displaying agents, e.g., EVs, of interest bind to the same detection reagents, and to different capture reagents on two different solid phases, as illustrated in FIG. 33. Thus, in embodiments, the capture reagent (which may include the third barcode sequence and the first cleavage site), and the adaptor oligonucleotide (which may include the fourth barcode sequence and the second cleavage site) are different for the two different surface marker displaying agents, e.g., EVs, of interest, while the first and second binding reagents (and therefore the second and third barcode sequences) are the same for the two different surface marker displaying agents, e.g., EVs, of interest. In embodiments, the two different surface marker displaying agents, e.g., EVs, of interest are isolated separately by cleaving with the first restriction site for the first surface marker displaying agent, e.g., EV, then cleaving with the first restriction site for the second surface marker displaying agent, e.g., EV. In embodiments, the two different surface marker displaying agents, e.g., EVs, of interest are isolated separately by using two different types of solid phases (e.g., beads) that can be separated by size, gravity, magnetism (e.g., magnetic beads for the first surface marker displaying agent, e.g., EV and non-magnetic beads for the second surface marker displaying agent, e.g., EV), bead color, and the like. In embodiments, the two different surface marker displaying agents, e.g., EVs, of interest are isolated together by elution, and the first barcodes are used to distinguish between the two different surface marker displaying agents, e.g., EVs, since the first barcodes for the first and second surface marker displaying agents, e.g., EVs, are different. In embodiments, the second, third, and fourth barcodes can be sequenced to determine the total number of the two different types of surface marker displaying agents, e.g., EVs.

In embodiments, the method includes isolating two different surface marker displaying agents, e.g., EVs, of interest (i.e., first and second surface marker displaying agents, e.g., EVs) from the sample, wherein the two different surface marker displaying agents, e.g., EVs, of interest bind to one of the same binding reagents, and to different capture reagents and one different binding reagent on different solid supports, as illustrated in FIG. 34. Thus, in embodiments, the capture reagent (which may include the third barcode sequence and the first cleavage site), and one of the two binding reagents (which may include the first barcode sequence or the second barcode sequence), and the adaptor oligonucleotide (which may include the fourth barcode sequence, the second cleavage site, and the complementary nucleotide sequence to the anchoring oligonucleotide) are different for the two surface marker displaying agents, e.g., EVs, of interest, while the other of the two binding reagents (which may include the first barcode sequence or the second barcode sequence) are the same for the two different surface marker displaying agents, e.g., EVs, of interest. In embodiments, the second, third, and fourth barcodes can be sequenced to determine the relative ratio of the two different surface marker displaying agents, e.g., EVs, of interest in the sample.

In embodiments, the method includes isolating two different surface marker displaying agents, e.g., EVs, of interest (i.e., first and second surface marker displaying agents, e.g., EVs) from the sample, wherein the two different surface marker displaying agents, e.g., EVs, of interest bind to different capture reagents on different solid supports, and to different first and second binding reagents as illustrated in FIG. 35. Thus, in embodiments, the capture reagent (which may include the third barcode sequence and the first cleavage site), the first and second binding reagents (which may include the first and second barcode sequences), and the adaptor oligonucleotide (which may include the fourth barcode sequence, the second cleavage site, and the complementary nucleotide sequence to the anchoring oligonucleotide) are different for the two surface marker displaying agents, e.g., EVs, of interest. In embodiments, the second, third, and fourth barcodes can be sequenced to determine the relative ratio of the two different surface marker displaying agents, e.g., EVs, of interest in the sample.

In embodiments, the method includes isolating two different surface marker displaying agents, e.g., EVs, of interest (i.e., first and second surface marker displaying agents, e.g., EVs) from the sample, wherein the two different surface marker displaying agents, e.g., EVs, of interest bind to different capture reagents on different solid supports, and to different first and second binding reagents, and wherein the second oligonucleotide further includes a first amplification primer site before the second barcode sequence, and the adaptor oligonucleotide further includes a second amplification primer site after the fourth barcode sequence as illustrated in FIG. 36. Thus, in embodiments, the second, third, and fourth barcode sequences are joined together by extension and ligation of the first and second amplification primer sites.

In embodiments, the present disclosure provides a method of isolating a surface marker displaying agent of interest in a sample, comprising: contacting the sample with, and selectively binding the surface marker displaying agent of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences, and (ii) a capture reagent, wherein the capture reagent is linked to an anchoring reagent, wherein the anchoring reagent comprises: (1) a nucleotide sequence complementary to the second binding reagent nucleotide sequence and (2) at least one cleavage site, and wherein the anchoring reagent is bound to the surface; hybridizing the anchoring reagent with the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent, and the first and second binding reagents; and releasing the anchoring reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments, the present disclosure provides a method of isolating an EV of interest in a sample, comprising: contacting the sample with, and selectively binding the EV of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences, and (ii) a capture reagent, wherein the capture reagent is linked to an anchoring reagent, wherein the anchoring reagent comprises: (1) a nucleotide sequence complementary to the second binding reagent nucleotide sequence and (2) at least one cleavage site, and wherein the anchoring reagent is bound to the surface; hybridizing the anchoring reagent with the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV, and the first and second binding reagents; and releasing the anchoring reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.

In embodiments, the anchoring reagent comprises biotin, and the surface comprises streptavidin. In embodiments, the at least one cleavage site is a restriction site. In embodiments, the anchoring reagent comprises two cleavage sites. In embodiments, the anchoring reagent comprises two restriction sites.

In embodiments, the capture reagent is linked to the anchoring reagent with PEG, poly(A), or a polynucleotide sequence.

In embodiments, a method of isolating an EV of interest from a sample using multiple (e.g., three) markers and a single solid phase is illustrated in FIG. 31A. In embodiments, the first binding reagent includes a nucleotide sequence comprising a first amplification primer site, a first barcode sequence, and a complementary nucleotide sequence to the second binding reagent nucleotide sequence. In embodiments, the second binding reagent includes a nucleotide sequence comprising a complementary nucleotide sequence to the first binding reagent, a second barcode sequence, and a complementary nucleotide sequence to the anchoring reagent nucleotide sequence. In embodiments, the capture reagent is linked via a flexible linker to an anchoring reagent, and the anchoring reagent comprises two cleavage sites (e.g., first and second restriction sites), a second amplification primer site, a third barcode sequence, a complementary nucleotide sequence to the second binding reagent nucleotide sequence, and biotin. In embodiments, the anchoring reagent is anchored to a solid phase that comprises streptavidin.

Assaying the EV

In embodiments of the invention, the surface marker displaying agent of interest is assayed. In embodiments, the assay is an ultrasensitive assay. In embodiments of the invention, the surface marker displaying agent of interest is assayed while bound to the surface, either by both attachment points, e.g., by the capture reagent and by the binding reagent/anchoring reagent, or after the capture reagent is released from the surface. In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

In embodiments of the invention, the EV of interest is assayed. In embodiments, the assay is an ultrasensitive assay. In embodiments of the invention, the EV of interest is assayed while bound to the surface, either by both attachment points, e.g., by the capture reagent and by the binding reagent/anchoring reagent, or after the capture reagent is released from the surface. In embodiments, the assaying comprises contacting a detectably labeled oligonucleotide with the surface, wherein the oligonucleotide is complementary to the amplicon. In embodiments, the binding reagent is detectably labeled.

In embodiments of the invention, bound surface marker displaying agents, e.g., EVs, of interest are subjected to a measuring step, which are known to those of skill in the art, for example, as disclosed in International Appl. No. PCT/US2015/030925, published as WO 2015/175856, which is incorporated by reference in its entirety. This application describes an ultrasensitive assay format for soluble proteins that marry a variation of proximity ligation amplification (PLA) with ECL detection to provide state-of-the-art sensitivity. The measuring step of the method can comprise imaging an optical signal from the surface to generate an image that consists of a plurality of pixels, wherein each resolvable binding region maps to one or more pixels or groups of pixels in the image. Image analysis to identify pixels or sets of pixels having a signal indicative of a binding event (detection complex) can be accomplished using art recognized methods.

In one embodiment, the resolvable binding regions are elements of an array. In embodiments, the array is an array of micro-wells or nanowells, e.g., individual depressions or wells of a unitary substrate. Preferably, the volume of the wells is less than 500 uL, 300 uL, 150 uL, 100 uL, 10 uL, 1 uL, 100 nL, preferably less than 50 nL. In one embodiment, the volume of the wells ranges from approximately 10 aL-100 pL. Optionally, the wells may be configured to hold a microparticle.

In one embodiment, at least 50% of the resolvable binding regions positioned on a substrate and addressed during an assay contain either zero or one analyte molecule. Preferably, at least 80%, more preferably at least 95%, and most preferably at least 99% of the resolvable binding regions contain either zero or one analyte molecule. The concentration of analyte molecules in the sample is determined at least in part using a calibration curve, a Poisson distribution analysis and/or a Gaussian distribution analysis of the number of binding regions that contain at least one or one analyte molecule. In a specific embodiment, the surface comprises a plurality of particles each including a plurality of capture reagents for an analyte molecule and the plurality of particles is distributed across a plurality of resolvable binding regions (e.g., an array of micro- or nano-wells). Therefore, the method includes: (i) binding one or more analyte molecules to one or more capture reagents on the surface, (ii) distributing the plurality of particles across an array of resolvable binding regions; and (iii) determining the presence or absence of an analyte molecule in each resolvable binding regions, so as to identify the number of binding domains that contain an analyte molecule and/or the number of binding domains that do not contain an analyte molecule.

Alternatively, labels used to detect analyte molecules can be fluorescent species that can be used in single molecule fluorescence detection, e.g., fluorescence correlation spectroscopy, and/or fluorescence cross-correlation spectroscopy. Single molecule fluorescence detection comprises flowing an eluent that includes a detectable species through a capillary, focusing a light source on a volume within the capillary to create an interrogation zone and observing the interrogation zone with a light detector to detect the passage of fluorescent molecules through the interrogation zone.

In one embodiment, the surface marker displaying agent, e.g., EV, of interest in the sample may be measured using electrochemiluminescence-based assay formats, e.g. electrochemiluminescence (ECL) based immunoassays. Species that can be induced to emit ECL (ECL-active species) have been used as ECL labels, e.g., i) organometallic compounds where the metal is from, for example, the noble metals of group VIII, including Ru-containing and Os-containing organometallic compounds such as the tris-bipyridyl-ruthenium (RuBpy) moiety and ii) luminol and related compounds. Species that participate with the ECL label in the ECL process are referred to herein as ECL coreactants. Commonly used coreactants include tertiary amines (e.g., see U.S. Pat. No. 5,846,485 and U.S. Provisional Application No. 62/787,892, filed on Jan. 3, 2019), oxalate, and persulfate for ECL from RuBpy and hydrogen peroxide for ECL from luminol (see, e.g., U.S. Pat. No. 5,240,863). In embodiments, the ECL coreactant is tripropylamine (TPA). In embodiments, the ECL coreactant is N-Butyldiethanolamine (BDEA). In embodiments, the ECL coreactant is N,N-dibutylethanolamine (DBAE). In embodiments, the ECL coreactant is included in a read buffer for the ECL assay. In embodiments, the read buffer comprises an ECL coreactant and a surfactant. In embodiments, the surfactant is TRITON X-100. In embodiments, the read buffer does not comprise TRITON X-100. In embodiments, the surfactant does not disrupt a surface of the surface marker displaying agent. In embodiments, the surfactant does not disrupt a lipid bilayer membrane. In embodiments, the surfactant does not disrupt a membrane of an EV. In embodiments, the surfactant is BRIJ, TWEEN, PLURONIC or KOLLIPHOR. In embodiments, the surfactant is TWEEN. In embodiments, the read buffer does not comprise a surfactant.

The light generated by ECL labels can be used as a reporter signal in diagnostic procedures (Bard et al., U.S. Pat. No. 5,238,808, herein incorporated by reference). For instance, an ECL label can be covalently coupled to a binding agent such as an antibody, nucleic acid probe, receptor or ligand; the participation of the binding reagent in a binding interaction can be monitored by measuring ECL emitted from the ECL label. Alternatively, the ECL signal from an ECL-active compound may be indicative of the chemical environment (see, e.g., U.S. Pat. No. 5,641,623 which describes ECL assays that monitor the formation or destruction of ECL coreactants).

The methods of the invention may be applied to singleplex or multiplex formats where multiple assay measurements are performed on a single sample. Multiplex measurements that can be used with the invention include, but are not limited to, multiplex measurements i) that involve the use of multiple sensors; ii) that use discrete assay domains on a surface (e.g., an array) that are distinguishable based on location on the surface; iii) that involve the use of reagents coated on particles that are distinguishable based on a particle property such as size, shape, color, etc.; iv) that produce assay signals that are distinguishable based on optical properties (e.g., absorbance or emission spectrum) or v) that are based on temporal properties of assay signal (e.g., time, frequency or phase of a signal).

The invention includes methods for detecting and counting individual detection complexes. In a specific embodiment, the surface can comprise a plurality of capture reagents for one or more surface marker displaying agents, e.g., EVs, that are present in a sample and the plurality of capture reagents are distributed across a plurality of resolvable binding regions positioned on the surface. Under the conditions used to carry out and analyze a measurement, a “resolvable binding region” is the minimal surface area associated with an individual binding event that can be resolved and differentiated from another area in which an additional individual binding event is occurring. Therefore, the method consists of binding one or more surface marker displaying agents, e.g., EVs, of interest to one or more capture reagents on the surface, determining the presence or absence of the surface marker displaying agent, e.g., EV, in a plurality of resolvable binding regions on the surface, and identifying the number of resolvable binding regions that contain a surface marker displaying agent, e.g., EV, of interest and/or the number of analyte domains that do not contain a surface marker displaying agent, e.g., EV, of interest.

The resolvable binding regions can be optically interrogated, in whole or in part, i.e., each individual resolvable binding region can be individually optically interrogated and/or the entire surface comprising a plurality of resolvable binding regions can be imaged and one or more pixels or groupings of pixels within that image can be mapped to an individual resolvable binding region. A resolvable binding region may also be a microparticle within a plurality of microparticles. The resolvable binding regions exhibiting changes in their optical signature can be identified by a conventional optical detection system. Depending on the detected species (e.g., type of fluorescence entity, etc.) and the operative wavelengths, optical filters designed for a particular wavelength can be employed for optical interrogation of the resolvable binding regions. In embodiments where optical interrogation is used, the system can comprise more than one light source and/or a plurality of filters to adjust the wavelength and/or intensity of the light source. In some embodiments, the optical signal from a plurality of resolvable binding regions is captured using a CCD camera. Other non-limiting examples of camera imaging systems that can be used to capture images include charge injection devices (CIDs), complementary metal oxide semiconductors (CMOSs) devices, scientific CMOS (sCMOS) devices, and time delay integration (TDI) devices, as will be known to those of ordinary skill in the art. In some embodiments, a scanning mirror system coupled with a photodiode or photomultiplier tube (PMT) can be used for imaging.

Additional methods of interrogating whole surface marker displaying agents, e.g., EVs, are known in the art, such as by bioluminescence, and NMR. In additional embodiments, for example, the surface marker displaying agent, e.g., EV, of interest is assessed by quantitative polymerase chain reaction, next generation sequencing, or both.

Thus, an exemplary protocol for the methods described herein includes: coating a surface, e.g., a plate having a plurality of wells, each well comprising streptavidin, with a capture reagent, e.g., a biotinylated capture antibody, and incubating the biotinylated capture antibody on the plate, e.g., about 1 hour to about 12 hours; washing the plate, adding dilution buffer and a sample containing the EV of interest to the plate, and incubating the sample for about 1 hour to capture the EVs in the sample with the capture antibody; washing the plate, adding a detection reagent, e.g., a detection antibody, and incubating the sample with the detection antibody for about 1 hour to label the captured EVs; and washing the plate, adding assay buffer, and detecting the EVs labeled with the detection antibody with an instrument, e.g., an instrument configured to detect electrochemiluminescence.

In a multiplex variant of the exemplary protocol described above, the plate is coated with a plurality of different capture antibodies, which may capture different EVs of interest in one sample, and the different EVs of interest are detected with a common detection antibody. The multiplexed methods described herein advantageously allow the same sample containing multiple EVs of interest to be assayed in one experiment, which may help to reduce the amount of sample required and also decrease sample-to-sample variability. In embodiments, a multiplexed method is used to compare multiple capture reagents to the same target and facilitate selection of a preferred capture antibody.

Multiplex methods can also facilitate comparison of different EVs in a same sample, e.g., determining the relative abundance of different EVs. In embodiments, the relative abundance of EVs in a sample can be measured by using a plurality of different capture reagents to capture different EVs expressing different markers, then detecting each type of captured EVs with the same detection reagent to a common marker on the different EVs. In embodiments, the relative abundance of EVs in a sample can be measured by using the same capture reagent to capture different EVs expressing a common marker, then using a plurality of different detection reagents to determine the different markers expressed by the EVs.

Controls

In an additional embodiment, the assay format described herein further includes one or more control assays. A negative control can be included on a binding domain which includes a capture antibody that does not have a corresponding detection antibody, thereby providing a consistent background signal for all samples. Measurement of signal above a preset threshold value can indicate improper assay processing or the presence of a sample-dependent matrix effect causing non-specific binding of labeled detection probe. Moreover, a specimen control can also be included in the assay for a human target antigen (such as a secreted or intracellular protein) that performs multiple control functions. A positive signal will indicate the presence of human material, and therefore test for sample addition and quality. Measurement of a signal below a predefined threshold would indicate that no sample was added, that a failure in the reagents or process occurred, or that substances that interfere with amplification or detection are present. In addition to internal controls, external positive and negative controls can also be used with the method and/or kit. The negative control comprises a representative matrix without any target proteins.

In embodiments, a control surface marker displaying agent is used to establish the performance of the assay or provide a reliable sample for normalizing data, or both. In embodiments, control surface marker displaying agents facilitate comparison of results between plates or experiments, or both. In embodiments, a control surface marker displaying agent is used for correction of nonlinearity of an assay at upper and lower ends of the calibration curve.

In embodiments, a control EV is used to establish the performance of the assay or provide a reliable sample for normalizing data, or both. In embodiments, control EVs facilitate comparison of results between plates or experiments, or both. In embodiments, a control EV is used for correction of nonlinearity of an assay at upper and lower ends of the calibration curve. For example, it may be advantageous to utilize a synthetic EV, which allows for selection of surface antigens, and the copy number can be tuned to match the biological material of interest. In embodiments, the control EV has similar size and density to the EV of interest. In embodiments, the synthetic EV is produced using polymer beads of similar size and density to small EVs. In embodiments, tetraspanin proteins are attached to the surface of the synthetic EV.

In embodiments, well-characterized, biologically-derived EVs that are used as controls. In embodiments, control EVs are produced from a cell line selected for its efficiency at producing EVs. In embodiments, EVs from cell lines or biofluids are used as negative controls, such as from platelets, PBMCs, THP-1 cells, Expi293 cells, and HCT-15 cells. In embodiments, synthetic EVs, such as unilamellar vesicles or beads that have similar physiochemical properties as the EVs of interest, are used as controls.

Cargo Analysis

The invention further provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a liquid, or a combination thereof, encapsulated by a surface marker displaying agent of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; (b). binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest; and (d). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof. In embodiments, the assay is an ultrasensitive assay.

In additional embodiments, the invention provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or combination thereof, encapsulated by a surface marker displaying agent, comprising: (a). contacting the sample comprising an surface marker displaying agent with a surface, wherein the surface marker displaying agent encapsulates the target protein, nucleic acid or metabolite, and selectively binding the surface marker displaying agent to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the surface marker displaying agent, the binding reagent and anchoring oligonucleotide; (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest; and (e). conducting an assay to identify, quantitate, or both, the protein, nucleic acid, lipid, or combination thereof. In embodiments, the assay is an ultrasensitive assay.

The invention further provides a method of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by a surface marker displaying agent in a sample, comprising: (a). contacting the sample comprising a surface marker displaying agent with a surface, wherein the surface marker displaying agent encapsulates a protein, a nucleic acid, a lipid, or a combination thereof, and selectively binding the surface marker displaying agent to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent, and the binding reagent; (b). hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the surface marker displaying agent, the binding reagent, and the anchoring oligonucleotide; (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest; and (d). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, metabolite, or a combination thereof. In embodiments, the assay is an ultrasensitive assay.

In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

The invention further provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a liquid, or a combination thereof, encapsulated by an EV of interest in a sample, comprising: (a). contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; (b). binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and (d). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof. In embodiments, the assay is an ultrasensitive assay.

In additional embodiments, the invention provides methods of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or combination thereof, encapsulated by an EV, comprising: (a). contacting the sample comprising an EV with a surface, wherein the EV encapsulates the target protein, nucleic acid or metabolite, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; (b). binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; (c). hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent and anchoring oligonucleotide; (d). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and (e). conducting an assay to identify, quantitate, or both, the protein, nucleic acid, lipid, or combination thereof. In embodiments, the assay is an ultrasensitive assay.

The invention further provides a method of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV in a sample, comprising: (a). contacting the sample comprising an EV with a surface, wherein the EV encapsulates a protein, a nucleic acid, a lipid, or a combination thereof, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; (b). hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; (c). releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and (d). conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, metabolite, or a combination thereof. In embodiments, the assay is an ultrasensitive assay.

The contents of surface marker displaying agents, e.g., vesicles, vary with respect to mode of biogenesis, cell type, and physiologic conditions. In embodiments, the contents of surface marker displaying agents include proteins, nucleic acids, lipids, carbohydrates, small molecules such as hormones, cofactors, vitamins, minerals, salts, metals, metal-containing compounds, or combination thereof. In general, EVs encapsulate (i.e., are loaded with cargo) various proteins, lipids, nucleic acids and metabolites. The loading of the different types of cargo can be specific per vesicle and cell type. Research conducted to characterize the content of EVs has resulted in the assembly of different databases collecting the datasets from the many EV studies. Three different databases are publicly accessible: Exocarta, Vesiclepedia, and EVpedia (Kim et al., EVpedia: an integrated database of high-throughput data for systemic analyses of extracellular vesicles, J Extracell Vesicles 2:1-7 (2013); Kalra et al., Vesiclepedia: a compendium for extracellular vesicles with continuous community annotation, PLoS Biol. 2012; Mathivanan S, Simpson RJ. ExoCarta: a compendium of exosomal proteins and RNA, Proteomics 9:4997-5000 (2009); Simpson et al., ExoCarta as a resource for exosomal research, J Extracell Vesicles. 2012; Mathivanan et al., ExoCarta 2012: database of exosomal proteins RNA and lipids, Nucleic Acids Res. 2012, each of which is incorporated by reference in its entirety). All databases include the protein, nucleic acid, and lipid content together with the isolation and purification procedures used to generate the data.

In embodiments, the protein that is encapsulated within the EV is of CNS cell origin, for example, neuron, astrocyte, oligodendrocyte, or microglia cells. Exemplary proteins include, but are not limited to, TSG101, HSP70, ALIX/PDCD6IP, Flotillin, Tuj 1, Tyr hydroxylase, NSE, NF-L, GFAP, S100β, GluSyn, CNPase, Oligo2, TMEM119, or a combination thereof.

In embodiments exemplified in FIG. 4A, the encapsulated molecules within the EV of interest are subjected to an assay, e.g., an ultrasensitive assay, that comprises lysing the EV, and conducting an assay on the lysate. In embodiments, assays may comprise additional steps to digest non-EV associated proteins, as exemplified in FIG. 4B. Such a method may include contacting the surface with a protease, inactivating the protease, lysing the EV and transferring the lysate to a second surface, wherein the lysate is detected, analyzed or both using an assay. Assays for proteins, oligonucleotides and lipids are well known in the art. In embodiments, the EV of interest encapsulates a protein, a nucleic acid, a lipid, or a combination thereof. In embodiments, the nucleic acid is RNA. In embodiments the RNA is a mature miRNA.

Many biomarkers proposed in the CNS-EV literature are expected to originate within the cytosol of neurons or glia and be secreted inside EVs as “cargo”. The concentration of these cargo proteins can be exceedingly low, and the difficulty of making accurate measurements can be compounded by the existence of non-EV associated (soluble) forms of the same protein in biofluid samples. To a first approximation, EVs are found in human plasma at a concentration of about 1×10¹⁰ particles/mL and CNS-EVs should represent only a small fraction of all EVs. For measurements of a cargo protein in a specific population of CNS-EVs representing 0.1% of the total EVs in circulation, assuming that each CNS-EV has a single copy of the target protein, a concentration of <1 pg/mL for a protein of average molecular weight would be expected, which is generally below the sensitivity of conventional assays. Thus ultrasensitive assays are usually required to detect, measure, or both, these low concentration analytes.

Ultrasensitive assay format for soluble proteins that marry a variation of proximity ligation amplification with ECL detection to provide state-of-the-art sensitivity for protein assays are known in the art, see, e.g., as disclosed in International Appl. No. PCT/US2015/030925, published as WO 2015/175856. Such assays have detection limits as low as the pg/mL to sub pg/mL level, detecting as low as 1000 molecules per 25 uL sample.

In embodiments, to verify the identity of the EVs isolated using each specific surface marker signature, cargo proteins specifically expressed in each of the CNS-EV types are identified and measured. In embodiments, EV surface proteins are identified and measured, for example, if no specific intracellular proteins are available for a cell type, but they should not be one of the same proteins used in the specific EV isolation.

Kits

The invention further provides kits for isolating, detecting, measuring, or combinations thereof, a surface marker displaying agent in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising (i) a capture reagent for the surface marker displaying agent, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring reagent; and (b) a binding reagent for the surface marker displaying agent.

The invention further provides kits for detecting a surface marker displaying agent in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising (i) a capture reagent for the surface marker displaying agent, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring oligonucleotide; (b) binding reagent for the surface marker displaying agent that is linked to a primer oligonucleotide; and (c) a circular oligonucleotide template comprising a sequence complementary to the primer oligonucleotide.

In embodiments, the surface marker displaying agent is a cell. In embodiments, the surface marker displaying agent is a virus or viral particle. In embodiments, the surface marker displaying agent is an organelle. In embodiments, the surface marker displaying agent is a vesicle. In embodiments, the surface marker displaying agent is an extracellular vesicle or exosome.

The invention further provides kits for isolating, detecting, measuring, or combinations thereof, an EV in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring reagent; and (b) a binding reagent for the EV.

The invention further provides kits for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring oligonucleotide; (b) binding reagent for the EV that is linked to a primer oligonucleotide; and (c) a circular oligonucleotide template comprising a sequence complementary to the primer oligonucleotide.

In embodiments, the disclosure further provides a kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising a binding domain; (b) a linking reagent capable of binding to the binding domain; and (c) an anchoring reagent capable of binding to the binding domain. In embodiments, the kit further comprises a capture reagent for a surface marker, e.g., an EV surface marker, wherein the capture reagent is capable of binding to the linking reagent.

In embodiments, the disclosure further provides a kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: (a) a surface comprising a targeting reagent complement in a binding domain; (b) a linking reagent connected to a targeting reagent, wherein the targeting reagent is a binding partner of the targeting reagent complement; and (c) an anchoring reagent comprising a supplemental linking reagent, wherein the supplemental linking reagent is capable of binding to the linking reagent. In embodiments, the kit further comprises a capture reagent for a surface marker, e.g., an EV surface marker, wherein the capture reagent comprises a supplemental linking reagent capable of binding to the linking reagent.

In embodiments, the surface comprises a plurality of binding domains, wherein each binding domain comprises a different targeting reagent complement; and wherein the kit further comprises a plurality of linking reagents, each linking reagent connected to a different targeting reagent for each of the different targeting reagent complements. In embodiments, the kit further comprises a plurality of capture reagents, each capture reagent comprising a supplemental linking reagent capable of binding to the linking reagent. Exemplary surfaces are described in, e.g., U.S. Pat. Nos. 10,201,812; 7,842,246 and 6,977,722, the disclosures of which are hereby incorporated by reference in their entireties.

In embodiments of a kit comprising a plurality of binding domains, the kit further comprises a plurality of capture reagents, each capture reagent comprising a supplemental linking reagent capable of binding to the linking reagent. In embodiments, the surface comprises an array with a plurality of different targeting reagent complements immobilized on one or more solid phase supports, each array element comprising a different targeting reagent complement, and each of the different targeting reagent complements being the binding partner of a different targeting reagent. In embodiments, the capture reagents are connected to one of the different targeting reagents, and each of the capture reagents is connected to a different targeting reagent. Furthermore, the anchoring reagent is divided into a plurality of portions each having at least a copy of the anchoring reagent, and the anchoring reagent in each portion is connected to a different targeting reagent. Thus, in embodiments, the solid phase support comprises a targeting reagent complement, and each of the capture reagent and anchoring reagent comprises a targeting reagent. In embodiments, each capture reagent and anchoring reagent portion may be provided separately, all reagents/portions linked to the same targeting reagent are provided as a mixture and separate from the other reagents, all capture reagents are provided as a mixture and all anchor reagent portions are provided as a mixture, or all capture reagents and anchor reagent portions are provided as one mixture.

In embodiments, the capture reagent comprises a supplemental linking reagent; the anchoring reagent comprises a supplemental linking reagent; the targeting reagents are connected to a linking reagent; and the linking reagent is a binding partner of the supplemental linking reagent. Thus, in embodiments, the surface comprises a targeting reagent complement, which binds to the targeting reagent that is connected to the linking reagent, which binds to the supplemental linking reagent on the capture reagent and anchoring reagent.

In embodiments, the targeting reagent and targeting reagent complement are two members of a binding partner pair selected from avidin-biotin, streptavidin-biotin, antibody-hapten, antibody-antigen, antibody-epitope tag, nucleic acid-complementary nucleic acid, aptamer-aptamer target, and receptor-ligand. In embodiments, the targeting reagent is biotin and the targeting reagent complement is streptavidin. In embodiments, the linking reagent and supplemental linking reagent pair is a different binding partner pair than the targeting reagent and targeting reagent complement pair. In embodiments, the linking reagent is avidin or streptavidin, and the supplemental linking reagent is biotin. In embodiments, the targeting reagent and targeting reagent complement are complementary oligonucleotides.

In embodiments, the linking reagent and supplemental linking reagent are two members of a binding partner pair selected from avidin-biotin, streptavidin-biotin, antibody-hapten, antibody-antigen, antibody-epitope tag, nucleic acid-complementary nucleic acid, aptamer-aptamer target, and receptor-ligand. In embodiments, the linking reagent is biotin and the supplemental linking reagent is streptavidin. In embodiments, the linking reagent is avidin or streptavidin, and the supplemental linking reagent is biotin.

In embodiments, the array comprising the plurality of binding domains is on one solid phase support, and the solid phase support is an electrode. In embodiments, the solid phase support is a carbon-based electrode. In embodiments, the kit comprises a multi-well plate assay consumable, and each well of the plate comprises a carbon ink electrode. In some embodiments, the solid phase supports are particles. In embodiments, each element of the array is on a different solid phase support, and the solid phase supports are beads.

In embodiments, the anchoring reagent includes an anchoring sequence that is directly or indirectly bound (e.g., through binding reactions) to the surface. In embodiments, the anchoring reagent comprises a protein linked or otherwise bound to the anchoring sequence. In embodiments, any protein can be used that can be immobilized on a surface (covalently or non-covalently) and modified by an anchoring oligonucleotide. Non-limiting examples include streptavidin, avidin, or bovine serum albumin (BSA). In embodiments, the anchoring reagent comprises BSA. Methods of immobilizing anchoring reagents are described in, e.g., WO 2015/175856, herein incorporated by reference in its entirety.

In embodiments, the capture reagent in the kit comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or aptamer. In embodiments, the binding reagent in the kit comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or aptamer. In embodiments, both the capture reagent and the binding reagent are antibodies, or an epitope binding portion of an antibody.

In additional embodiments, the surface of the kit comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent, e.g., anchoring oligonucleotide, are located on two distinct binding domains on the surface. In further embodiments, the surface of the kit comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent, e.g., anchoring oligonucleotide are located on the same binding domain on the surface. In additional embodiments, the surface comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent, e.g., anchoring oligonucleotide are located on the same binding domain.

In embodiments, the kit comprises a surface wherein the capture reagent and the anchoring reagent, e.g., anchoring oligonucleotide are within 10 μm, 5 μm, or 100 nm on the surface.

In embodiments, the surface in the kit comprises an electrode.

In embodiments, the capture reagent comprised in the kit binds a common target protein to a specific type of surface marker displaying agents (e.g., a common marker for all cells, viruses, organelles, or vesicles). In embodiments, the capture reagent comprised in the kit binds a common EV target protein selected from CD9, CD37, CD63, CD81, CD82.

In embodiments, the kit comprises one or more buffers. In embodiments, the kit comprises one or more of a wash buffer, an assay buffer, and a read buffer. In embodiments, the same buffer can be used for the wash, assay, and detection (i.e., “read”) steps. In embodiments, the kit comprises a Tris buffer and/or a phosphate buffer. Non-limiting examples of wash buffers, assay buffers, and/or read buffers include phosphate buffer, Tris buffer, HEPES buffer, and the like. In embodiments, the wash buffer and/or the read buffer comprises a surfactant. In some embodiments, the surfactant is TRITON-X. In embodiments, the surfactant is TWEEN-20. In embodiments, the wash buffer and/or the read buffer comprises a co-reactant. In embodiments, the co-reactant is tripropylamine (TPA). In embodiments, the read buffer is a Tris buffer comprising TRITON-X and TPA. In embodiments, the read buffer comprises N-Butyldiethanolamine (BDEA). In embodiments, the read buffer comprises N,N-dibutylethanolamine (DBAE). In embodiments, the read buffer comprises a surfactant that does not disrupt a surface of the surface marker displaying agent. In embodiments, the read buffer comprises a surfactant that does not disrupt a lipid bilayer membrane. In embodiments, the read buffer comprises a surfactant that does not disrupt a membrane of an EV. In embodiments, the surfactant is BRIJ, TWEEN, PLURONIC or KOLLIPHOR. In embodiments, the read buffer does not comprise a surfactant. In embodiments, the read buffer is a read buffer provided in, e.g., U.S. Provisional Application No. 62/787,892, filed on Jan. 3, 2019.

Automated High Throughput EV Isolation and Cargo Screening

The invention further provides an automated version of the methods of the invention using a high-throughput robotic liquid handling system. This system allows simultaneous preparation of up to 480 samples with accuracy and reproducibility unmatched by a human operator. In embodiments, the automated system is a free-standing, fully integrated system for carrying out immunoassays using ECL technology. This system, capable of simultaneously running up to five 96-well assay plates, consists of a robotic lab automation workstation for liquid handling and plate manipulation, physically integrated with an ECL reader.

In embodiments, the workflow conducts the methods of the invention with minimal human intervention. In embodiments, a single 96-well source plate is loaded with 120 uL each of 96 plasma samples in each well. 25 uL per sample is dispensed along with appropriate diluents into each of four different capture plates, each for isolating a single CNS-EV type. Plates are incubated about two hours on shakers while EVs are captured. Next, the plates are washed and the binding reagents are then added and incubated for about one hour. Plates are washed again followed by addition of reagents for staple amplification and 15 minute incubation for stapling. Plates are washed again followed by addition of elution reagent for removing non-stapled EVs. After a final wash, each of the four plates contain a unique type of CNS EVs. Lysis buffer is optionally added to each well followed by a short incubation. Lysates from each plate are transferred along with appropriate diluents to one of four identical 4-plex cargo assay plates and the standard assay, e.g., ultrasensitive assay, procedure then follows to complete the assays. At the end of an about an 8 hour day each of the 96 samples are fractionated into 4 EV types and each type assayed for four different EV cargo analytes. The operator only has to set up the source plate, and load reagents into the instrument. No further intervention is required. In embodiments, the procedure is run three days in a row on the same samples with the same plate and reagent lots to assess run-to-run variability.

Screening for Multiple Markers to a Same Target

One of the challenges associated with multi-marker isolation (i.e., using two or more capture and/or detection reagents) of target molecules, for example, macromolecules such as proteins, protein complexes, surface marker displaying agents, or extracellular vesicles (EVs), is the need to efficiently identify multi-marker signatures that correspond to the targets of interest. Multiple markers may need to be identified in any immunoassay requiring three or more binding reagents on a single protein, protein complex, large macromolecule such as EVs, or surface marker displaying agents such as cells, viruses, organelles, or vesicles. For example, multiple binding reagents may be desired for binding to different epitopes on the same protein. Multiple binding reagents may also be desired for binding to different surface markers on the same EV. Multiple binding reagents may further be desired for binding to different surface markers on the same surface marker displaying agent. In another example, multiple binding reagents may be desired for binding to the same epitope in a multimeric target (e.g., protein or protein complex), and it may be desirable to use one or more of the same binding reagents for binding to the same epitope in different monomers of the multimeric target. The present disclosure provides methods of screening large libraries of binding reagents to identify combinations of binding reagents that bind to the same target. In embodiments, the target is a surface marker displaying agent, and the binding reagents can target different surface markers (e.g., proteins) on the same surface marker displaying agent. In embodiments, the target is an EV, and the binding reagents can target different surface markers (e.g., proteins) on the same EV. In embodiments, the target is a large macromolecule, for example, a single protein, and the binding reagents can target different epitopes on the same protein. In embodiments, the target is a protein complex comprising one or more of the same protein monomers, and the binding reagents can target the same epitope on different monomers.

Accordingly, the present disclosure also provides methods of determining target epitopes on proteins, comprising: contacting the protein with a plurality of unique binding reagents, wherein each unique binding reagent comprises a detection sequence comprising a unique barcode oligonucleotide sequence, wherein if at least three unique binding reagents bind to three unique protein epitopes, an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the three unique binding reagents; and sequencing the output oligonucleotide to identify the barcode oligonucleotide sequences, thereby determining the at least three unique target protein epitopes.

Accordingly, the present disclosure also provides methods of determining surface markers of a surface marker displaying agent, comprising: contacting the surface marker displaying agent with a plurality of unique binding reagents, wherein each unique binding reagent comprises a detection sequence comprising a unique barcode oligonucleotide sequence, wherein if at least three unique binding reagents bind to three unique surface markers of a surface marker displaying agent, an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the three unique binding reagents; and sequencing the output oligonucleotide to identify the barcode oligonucleotide sequences, thereby determining the at least three unique surface markers of a surface marker displaying agent.

The present disclosure also provides methods of determining EV surface markers, comprising: contacting the EV with a plurality of unique binding reagents, wherein each unique binding reagent comprises a detection sequence comprising a unique barcode oligonucleotide sequence, wherein if at least three unique binding reagents bind to three unique EV surface markers, an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the three unique binding reagents; and sequencing the output oligonucleotide to identify the barcode oligonucleotide sequences, thereby determining the at least three unique EV surface markers.

In embodiments, at least one of the plurality of binding reagents comprises a detection sequence that comprises a hybridization sequence that is complementary to at least a portion of the detection oligonucleotide sequence of at least one other binding reagent.

In embodiments, the plurality of binding reagents comprises: a first binding reagent comprising a first detection sequence that comprises a first hybridization sequence, and a first amplification primer site; a second binding reagent comprising a second detection sequence that comprises a second hybridization sequence, and a third hybridization sequence; and a third binding reagent comprising a third detection sequence that comprises a fourth hybridization sequence, and a second amplification primer site, wherein the first hybridization sequence and the second hybridization sequence are complementary; wherein the third hybridization sequence and the fourth hybridization sequence complementary; and wherein generating the single output oligonucleotide comprises ligating, amplifying, or both, the hybridized first detection sequence, second detection sequence, and third detection sequence.

In embodiments, the plurality of unique binding reagents comprises at least ten unique binding reagents. In embodiments, the plurality of unique binding reagents comprises about 10 to about 100 unique binding reagents.

In embodiments, the sequencing is performed by next-generation sequencing. In embodiments, sequencing the output oligonucleotide comprises: adding one or more adapter sequences to the single output oligonucleotide; and sequencing the single output oligonucleotide using the adapter sequence.

In embodiments, the multiplexed method is conducted in solution.

In embodiments, the methods described herein enable combinatorial screening of more than 10, more than 20, more than 30, more than 40, more than 50, more than 60, more than 70, more than 80, more than 90, more than 100, more than 500, or more than 1000 binding reagents (e.g., antibodies) for EV surface markers in a single reaction. Thus, in embodiments, at least 10³, 20³, 30³, 40³, 50³, 60³, 70³, 80³, 90³, 100³, 500³, or 1000³ possible three-marker combinations can be screened in a single reaction. In embodiments, the multiple (e.g., three) binding reagents also serve as a secondary tether, allowing selective removal of EVs lacking the combination of the three surface markers, thereby providing additional specificity.

In embodiments, the surface markers are identified by next-generation sequencing of the barcode oligonucleotide sequences associated with the binding reagents specific for the surface markers. In embodiments, the same multiple (e.g., three) binding reagents (e.g., antibodies) identified by next-generation sequence are used for isolation of the surface marker displaying agent, e.g., EV, thereby simplifying reagent preparation and ensuring that the binding reagents (e.g., antibodies) behave similarly during both screening and isolation processes.

In embodiments, the EVs are isolated from monocytes. In embodiments, the EVs are isolated from B cells. In embodiments, the EVs are isolated from CD4+ T cells. In embodiments, the EVs are isolated from CD8+ T cells. In embodiments, the EVs are isolated from vascular endothelial cells.

A non-limiting, exemplary process for a method of determining surface markers on a target is illustrated in FIGS. 31A-31B. The process illustrated in FIGS. 31A and 31B is not limited to EVs, but can also be used with surface marker displaying agents described herein and includes:

1. Creating a binding reagent library. This includes coupling binding reagents to three different types of detection sequences to generate a first binding reagent, a second binding reagent, and a third binding reagent, each of which has a unique barcode oligonucleotide sequence. The detection sequences may be coupled to the binding reagents via flexible linkers, or coupled directly to the binding reagent. In embodiments, the binding reagent is an aptamer, and a single oligonucleotide is synthesized containing the aptamer and the detection sequence.

In embodiments, each binding reagent in the binding reagent library is coupled to each of the three types of detection sequences, in order to allow all combinations of three binding reagents to be tested. In embodiments, the combinations of three binding reagents comprise three different binding reagents. In embodiments, the combinations of three binding reagents comprise two or more of the same binding reagent, wherein each binding reagent is coupled to each of the three types of detection sequences. In embodiments, the combination of three binding reagents comprise three of the same binding reagent, wherein each binding reagent is coupled to each of the three types of detection sequences. In embodiments, the barcode oligonucleotide sequence is unique to each binding reagent-detection sequence combination, allowing the binding reagent to be identified by sequencing.

2. Contacting the binding reagent library with the target and incubating to allow binding of the binding reagents to the EV.

3. Capturing the target bound to the binding reagents and washing away unbound binding reagents. The binding reagent can be captured, for example, if one of the three binding reagents is biotinylated, to a solid support (e.g., a bead or surface) coated with streptavidin. The target can also be captured, for example, using an additional, common binding marker, such as a tetraspanin on an EV. In embodiments, a stringent wash is used to disrupt interactions between the detection sequences.

4. Wherein at least one first binding reagent, one second binding reagent, and one third binding reagent is bound to the same target (e.g., EV or protein), complementary regions of the detection sequences hybridize (see, e.g., FIG. 31A).

5. Adding polymerase and ligase to the reaction mixture to join the first, second, and third detection sequences, creating a single output oligonucleotide that includes all three barcode sequences (see, e.g., FIG. 31B).

6. Amplifying the single output oligonucleotide and incorporating sequencing primer sites.

7. Sequencing the single output oligonucleotides to identify combinations of the barcode oligonucleotide sequences.

In embodiments, the first detection sequence comprises a first amplification primer site and a first hybridization sequence. In embodiments, the second detection sequence comprises a second hybridization sequence and a third hybridization sequence. In embodiments, the third detection sequence comprises a fourth hybridization sequence and a second amplification primer site. In embodiments, the first hybridization sequence and the second hybridization sequences are complementary. In embodiments, the third hybridization sequence and the fourth hybridization sequences are complementary. Thus, in embodiments, the first and third detection sequences can each hybridize to the second detection sequence. In embodiments, after the first and third detection sequences hybridize to the second detection sequence, ligase is added to ligate the first, second, and third detection sequences into a single output oligonucleotide. In embodiments, after ligation, polymerase is added to remove any gaps in the ligated sequence and amplify the output oligonucleotide using the first and second amplification primer sites. In embodiments, the ligation and amplification are added at the same time (e.g., proximity ligation/extension). In embodiments, the amplification further comprises adding one or more sequencing primer sites to the ends of the output oligonucleotide. In embodiments, sequencing is performed using the sequencing primer sites.

Each sequencing read contains three barcode oligonucleotide sequences, which will be mapped to the identity of the binding reagent. In embodiments, the frequency of a specific combination of binding reagents will be related to the abundance of the three markers (e.g., surface markers on an EV or epitopes on a protein). In embodiments, the abundance of a single marker (e.g., surface markers on an EV or epitopes on a protein) can be determined from the frequency with which the marker is identified from the barcode oligonucleotide sequencing results. In embodiments, multiple binding reagents targeting the same marker can be compared using the barcode oligonucleotide sequencing results. For example, the highest affinity binding reagent can be identified as the binding reagent most represented by its barcode in the sequencing data.

In embodiments, the sequencing is performed with high-throughput sequencing. In embodiments, the sequencing produces at least 10⁶ reads. In embodiments, the sequencing produces at least 10⁷ reads. In embodiments, the sequencing produces at least 10⁸ reads. In embodiments, the sequencing produces at least 10⁹ reads.

III. Examples Example 1. Methods of Extracellular Vesicle (EV) Capture Example 1.1. Plate-Based Solid Phase Immunoaffinity Capture

Exosomes and other EVs can be captured on a solid support using affinity ligands that target known protein or carbohydrate moieties on their surface. The moiety most often used is the tetraspanin proteins, which are hypothesized to be present on the surface of most EVs. It has been disclosed that various beads or microtiter plates can be used for immunoaffinity precipitation of EVs. A plate-based approach is preferred when many samples must be handled in parallel or when stringent washing is desired to remove non-specific binding, which may be more difficult to perform on beads.

Antibodies used to capture EVs from fluid samples were displayed on Meso Scale Discovery plates. Streptavidin gold plates were typically used to display biotinylated antibodies. In order to capture as many EVs as possible, large spot streptavidin gold plates were used (MSD GOLD Immunoassay Plates). The large capture area improved capture kinetics (because capture rate is proportional to surface area) and EV binding capacity. Plates with directly coated antibodies could also be used.

EVs from a typical sample of cell culture medium could also be captured on a large spot electrode within a few hours using antibodies targeting any of the three tetraspanin proteins. Depleted media and fresh (non-depleted) sample were assayed using tetraspanin sandwich assays, and signal from depleted media is plotted as a fraction of the signal in the fresh (non-depleted) sample. Results are shown in FIGS. 5A and 5B.

Example 1.2. Immunoaffinity Capture and Elution

EVs have been found to be difficult to elute from a solid phase once they have been captured by antibodies. This occurrence is mostly likely due to high avidity arising from multiple interactions between the capture antibodies and EV surface markers that can occur when the capture antibody is present at a high surface concentration.

Typical elution strategies involve lowering the pH to decrease the affinity of the antibody-antigen binding. When the valency of the interaction is high, lowering the individual antibody affinity may not lower the overall avidity sufficiently to allow efficient elution of the EVs, as demonstrated in FIGS. 6A and 6B. Elution efficiency was inversely proportional to capture antibody concentration. Decreasing the capture concentration also significantly decreases the binding capacity of the surface and slows the capture kinetics.

As exemplified in FIG. 7, EVs are captured by STAG labeled-capture antibodies via immunocapture onto a solid phase, e.g., a bead or plate. The capture antibodies are immobilized on the solid surface with a cleavable linker or a double-stranded DNA (dsDNA) linker. The linker is then cleaved, or the dsDNA is denatured, to elute the EVs still bound to the capture antibodies. The capture antibodies are then either: eluted from the EVs using low pH, then the EVs can be used in assays or subjected to additional rounds of selection using other markers; or remain bound to the EVs and serve as detection antibodies in the assay using the STAG label.

Example 1.3. Bead-Based Immunoaffinity Capture

In this Example, solid-phase immunoaffinity capture was performed using beads as the solid phase. CD81 antibodies and a non-specific isotype matched antibody were separately immobilized on beads, and each antibody was incubated with exosomes isolated from normal human serum by PEG precipitation. The exosomes were then eluted at low pH and assayed with CD63, CD81, and CD9 sandwich assays. The non-depleted sample, the depleted sample, and the eluted fraction were all assayed.

Results are shown in FIG. 8. More than 98% of the EV-associated CD81 was depleted from the sample by the CD81 beads. Only approximately 1/3 of the captured EVs were eluted and subsequently recaptured, most likely due to inefficient elution.

Example 2. Sandwich Immunoassay Formats for Intact EVs

Immunoassay formats and methods for characterizing intact EVs based on surface protein or carbohydrate markers are described in Examples 2.1-2.4.

The following is an overview of the method for quantifying EVs or EV-associated proteins using ECL-based sandwich immunoassays.

Capture antibodies with reactivity to suspected EV-associated proteins are displayed on the surface of MSD plate electrodes, using either direct coating, biotinylated antibodies on streptavidin-coated plates, or a multispot system as described in U.S. Pat. Nos. 10,201,812; 7,842,246 and 6,977,722 (the disclosure of which are hereby incorporated by reference in their entireties), to display the capture antibodies.

A fluid sample suspected to contain EVs and particularly exosomes is applied to the surface. The wells of the plate may be prefilled with a small amount of a diluent to improve the assay characteristics. Many surfactants will disrupt the membranes of EVs should be considered when selecting diluent composition. Most often, DPBS with 2% bovine serum albumin is used as the assay diluent and added at a ratio of 1:1 with the sample (see Example 5.1 for further description of diluent composition). The plate is then incubated to allow EVs to be captured by the capture antibodies. The depletion of EVs from the sample is diffusion-limited due to the size of the EVs, thus, the time required to deplete the sample of EVs is dependent on spot size, EV size, plate agitation, and capture antibody concentration. Typically, a sample can be >90% depleted by a large spot plate in 2 hours, while a small spot plate may take 4 to 8 hours, and a 10-spot plate may take longer than 12 hours. A short capture time (1 hour) is typically used, particularly when a large number of EVs are expected to be in the sample, because complete depletion of EVs is impractical.

The plate is washed with water, or preferably a wash buffer, most preferably containing a small amount of Tween-20 (0.05% v/v) to aid in removal of physisorbed EVs from the plate surface.

Detection antibody is added in a diluent and incubated for a sufficient time to allow a significant fraction of the bound exosomes to be decorated. This detection antibody can target the same protein species as the capture antibody or a different protein. Where the same protein is targeted by both capture and detector antibodies, it is preferable to use the same clone or two clones that target the same epitope. This ensures that soluble monomeric protein will not be detected and minimizes the false positive signal that may be generated if the protein of interest is present in a dimerized or aggregated form. Certain diluent compositions may also reduce the false positive signal generated by soluble dimers (see Example 5.1). Where different species are targeted by the capture and detection antibodies, it is preferable to target two species that are known to not form heterodimers or higher order structures with one another, as the co-localization of the two proteins should only occur when both are embedded in an EV membrane. For samples with high soluble levels of one of the species used for capture or detection, a purification method such as ultrafiltration, ultracentrifugation, precipitation, or size exclusion chromatography should be used to reduce the soluble protein to avoid competition and the potential for false positive signals.

The most commonly used proteins for capturing and detection EVs are CD81, CD63 and CD9, so-called tetraspanin proteins because they have 4 membrane spanning alpha-helices. One or more of these proteins are believed to be present on nearly all EVs.

Example 2.1.1. Intact EV Sandwich Assays for CD63+ EVs, CD81+ EVs, and CD9+ EVs

50 μL of 1 μg/mL biotinylated CD63, CD81, or CD9 antibodies were added to a small spot streptavidin plate and shaken overnight to be immobilized.

The plates were washed with PBST to remove unbound antibody. Unlike typical sandwich assays, these assays use the same epitope for the capture and detection antibodies, so any unbound capture antibody left in the well can compete with the detection antibody and cause a loss of signal. This is also true of any bound antibody that desorbs from the surface using the capture step.

A soaking/blocking step in diluent after the plate is coated with capture antibody was found to yield more consistent results. A shorter capture time also appeared to minimize this competition, as there is less time for the capture antibody to desorb.

After blocking, the plate is washed and 25 μL of diluent A is added to each well, followed by 25 μL of each sample. In the results (FIG. 11), the samples were a dilution series of cell conditioned medium from Expi293 cells, which produce a large number of EVs expressing a high level of CD81. These EVs also express the surface proteins CD9 and CD63 to a lesser degree.

The samples were incubated on a shaker at room temperature for 1 hour, followed by washing with PBST in a plate washer.

The detection antibodies (the same as the capture antibody in each case) were added at 1 μg/mL in 25 μL of diluent A and incubated on a shaker at room temperature for 1 hour, followed by a PBST wash. The plate was then read with read buffer B on a SECTOR imager.

As shown in FIGS. 9A-9C, CD63 and CD81 assays were largely unaffected by the presence of 10% fetal bovine serum, while the CD9 assay had some adverse reaction to FBS due to cross-reactivity of the detection antibody to bovine CD9.

Table 1 shows the LLODs, the maximum dilution factor of neat exosome standard that is detectable (2.5 standard deviations above background).

TABLE 1 LLODs for Intact EV Sandwich Assays. Hill Slope Hill Slope LLOD LLOD Assay (Dil A) (10% FBS) (Dil A) (10% FBS) CD63 1.05 1.08  166-fold 149-fold CD81 1.04 1.04 8830-fold 8940-fold  CD9 1.02 1.02 2220-fold 490-fold

Example 2.1.2. Intact EV Assays Measuring Concentrated Exosomes from THP-1 Cells

THP-1 cells were grown in serum-free conditions with PMA to induce monocyte-like differentiation. Cell conditioned medium was collected on Day 4 and concentrated approximately 10-fold using Nanosep 300 kDa centrifugation units. Sample was serially diluted in 4-fold steps and assayed with each of the tetraspanin assays. Results are shown in FIG. 10 and demonstrate that the intact EV assays exhibit wide dynamics when used to measure concentrated exosomes from THP-1 cells. Table 2 is a summary of the LLODs.

TABLE 2 LLODs for Assays of Exosomes from THP-1 Cells. Hill LLOD LLOD LLOD Assay Slope (Dilution Factor) (Exosomes/mL) (Exosomes/well) CD63 1.02 3500-fold 6e7 1.5e6 CD81 0.97 2000-fold 1e8 2.5e6 CD9 1.05 2000-fold 1e8 2.5e6

Example 2.2 Two-Marker Assays for Intact EVs

Intact EV assays were run using all pairwise combinations of CD63, CD81, and CD9 as capture and detection antibodies.

Procedure:

CD63, CD81, and CD9 capture antibodies were each displayed in separate wells of a streptavidin gold plate or multispot plate. Samples were added and incubated to capture EVs with each of the tetraspanins. Plates were washed with PBST in a plate washer. Detection antibodies for CD63, CD81, CD9, or a cocktail of all three were added to various wells of the plate to yield all possible combinations of capture and detection antibodies.

Results are shown in FIG. 11. Interpretation of the signals is further discussed in Example 5.1. The signal roughly corresponds to the amount of the detection antibody target present on the population of EVs bearing the capture antibody target. For example, for CD81 capture/CD63 detection, the signal corresponds to the amount of CD63 protein present on the surface of all CD81+ vesicles.

Example 2.2.1. Screening Cell Supernatants and Purified Exosomes

Cell conditioned media (CCM) samples and EVs purified by differential ultracentrifugation were assayed for all combinations of CD63, CD81, CD9, and EpCAM (except EpCAM/EpCAM) as capture and detection antibody.

Results are shown in FIG. 12. Very different patterns for two-marker assay reactivity between the cell lines were observed. For the Panc-1 and HUVEC EVs, the pattern of reactivity is remarkably similar between the CCM and purified EVs, although the EVs have not been concentrated. For the tumor-derived exosomes, a significant change was observed, i.e., all CD81+ EVs were lost during ultracentrifugation. Notably, the HUVEC CCM and exosomes had no detectable EpCAM+ EVs, while all other samples had detectable levels of EpCAM+ EVs, which was expected because HUVEC are endothelial cells and do not typically express EpCAM.

Example 2.2.2. Use of Isotype Control Antibodies

Isotype control antibodies are frequently used in flow cytometry to assess non-specific binding of the antibody to the cell surface. Isotype control antibodies were used to assess non-specific binding of EVs to capture antibodies, and also used to assess non-specific binding of detection antibodies to specifically captured exosomes. These isotype control antibodies are typically raised against the KLH antigen. Antibodies raised against other antigens not expected to be present in the sample have also been used with success.

As illustrated in FIG. 13A, tetraspanin capture antibody was combined with isotype-matched non-specific control antibody detector to assess non-specific binding of detection antibodies to specifically-captured EVs.

As illustrated in FIG. 13B, isotype-matched non-specific control antibody was displayed on a plate as capture antibody and combined with tetraspanin detection antibodies to assess non-specific binding of exosomes to the surface, which were then specifically detected.

The results in FIG. 13C show low non-specific binding of EVs to IgG1-control capture antibody (last column), and low binding of IgG1-control antibody to captured EVs (4^(th) row).

Example 2.3.1. Multiplexed Assays for Common Markers on Intact EVs

The capture antibodies targeting CD63, CD81, and CD9 were displayed within the same well using the multispot system as described in U.S. Pat. Nos. 10,201,812; 7,842,246 and 6,977,722 (the disclosures of which are hereby incorporated by reference in their entireties). Spots 1, 3, and 8 were used due to their radial symmetry, and similar mass-transport should occur during mixing.

A 4-fold dilution series of Expi293 cell conditioned medium was generated, and assays were performed using all pairwise combinations of tetraspanin capture and detection antibodies. Easy assay was performed in singleplex as well as in a multiplex with all three capture antibodies in each well, but only a single detection antibody in each well.

FIG. 14 shows the ratios of the multiplex signal to the singleplex. In most cases, the signal for the multiplexed assays is within 10% of the singleplex assays.

Example 2.3.2. Multiplexed Assays for Rare EVs

Specific populations of EVs have been proposed as biomarkers of disease. Often, these populations are a small fraction of the total EVs in a sample and are characterized by the presence of a surface marker that is absent from most EVs.

A powerful screening tool for biomarker discovery and quantitative comparison of rare EV populations between samples has been developed by multiplexing capture antibodies for up to 10 surface antigens and then using common detector antibodies (tetraspanins or other common markers) for detection.

(A). Cell Line Screening with EV Cancer Markers

To develop a 10-plex of assays for tumor-associated EVs, 16 antibodies were arrayed against 13 different antigens suspected to be present on tumor-derived EVs in two 8-plexes.

Supernatants from 15 different culture conditions representing 10 different cell lines were assayed. Each sample was captured with both 8-plexes and detected with each of the tetraspanin detection antibodies separately.

Cell lines that produced EVs with 11 of the 13 markers were identified. See FIG. 15.

(B). Pancreatic Cancer EV Screening

Control samples from pancreatic cancer-derived cell lines and patient derived xenograft models (PDX) cultures were screened using 10-plex of cancer antigen capture antibodies and triplex of tetraspanin capture antibodies. Detection was performed using a cocktail of all three tetraspanin antibodies to maximize signal and minimize the amount of sample required.

Results are shown in FIG. 16A. All of the markers were detectable in at least one of the control samples.

Plasma samples from 10 pancreatic ductal adenocarcinoma patients and 10 healthy controls were diluted 1:10 and assayed on both the 10-plex cancer antigen array and the tetraspanin triplex.

Results are shown in FIG. 16B. Most of the cancer antigen+ EV populations were barely detectable in most of the samples. A notable exception was CEA, which showed significant elevation in the PDAC patients relative to healthy controls. Some other markers had individual cancer patients with high signals, such as P-Cadherin, CA15.3 E-Cadherin, and CA125, which could be indicative of a particular phenotype of the tumor cells that produced the EVs.

Markers that were too low to detect in both the healthy subjects and PDAC patients (e.g., EphA2, CA50, EpCAM, EGFR, CA19-9) are good candidates for further screening with a high-sensitivity amplified assay (see Example 2.4).

(C). Multiplexing on Printed Plates

Samples of cell conditioned medium (CCM) and exosomes from various cell lines and serum pools were captured using three 6-plex panels of cancer antigens. Not all of these antigens are expected to be on the surface of EVs as some are secreted in a soluble form. The captured EVs were detected using a cocktail of tetraspanin detection antibodies.

Results are shown in FIG. 17. Surface markers EGFR, CA15-3, CA19-9 were detected in pancreatic cancer cell line samples.

Example 2.4. Amplified Assays for EV Surface Proteins

The following detection schemes that used rolling-circle amplification to boost the signal from surface antigens on captured EVs were demonstrated, as further discussed in Examples 2.4.1 and 2.4.2:

Single Detection Antibody with Rolling Circle Amplification (RCA): A single antibody conjugate is used to both splint the DNA ligation and prime the DNA extension for rolling circle amplification. This can also be performed using a preformed rolling circle template and omitting the ligation step.

Homo-Pair Proximity Ligation: The same tetraspanin antibody is used for proximity probe 1 (PP1) and proximity probe 2 (PP2) in a proximity ligation/rolling circle amplification reaction.

Hetero-Pair Proximity Ligation: Antibodies against two different surface antigens are used for PP1 and PP2, respectively, in a proximity ligation/rolling circle amplification reaction.

PLA/RCA Cocktail: A PP1 for each of the tetraspanins and a PP2 for each of the tetraspanins is combined (6 proximity probes in all) to allow all combinations of CD63, CD81, and CD9 to produce amplified signal.

Example 2.4.1. Singleplex Assays

(A). Single Antibody RCA Detection of EV-Associated Antigens

A dilution series of Expi293 cell conditioned medium (CCM) was captured on two plates with CD81 co-spotted with anchor oligonucleotide. Captured EVs were detected with STAG-labeled detection antibodies (CD63, CD81, or CD9) or PP2 conjugates (CD63, CD81, or CD9). RCA reaction was then performed on the plate with detection conjugates. The procedure is illustrated in FIG. 18A.

Results are shown in FIG. 18B. The assay shows linear amplification (50× for CD81, 200× for CD63 and CD9) across a wide range of dilutions with no observable elevation in background signal. The low amplification ratio for CD81 is likely due to low labeling ratio of CD81-PP2 conjugate, the presence of unconjugated antibody, or competition by desorbed capture antibody.

(B). Homo- and Hetero-Pair Proximity Ligation/RCA for EV Surface Antigens

Expi293 EVs were captured on CD81 capture plates with anchor oligonucleotide and detected with all pairwise combinations of CD63, CD81, and CD9 PP1 and CD63, CD81, and CD9 PP2. The procedures for a homo-pair and a hetero-pair of proximity probes are illustrated in FIGS. 19A and 19B, respectively.

Results are shown in FIG. 19C. Low non-specific binding (ECL signal of 250 or less) was observed for all combinations of proximity probes.

(C). PLA/RCA Cocktail

EVs from 4 CCM samples were captured on plates printed with an anti-EphA2 capture antibody. MCO2 (PANC-1) and HCT-15 cells were expected to express high levels of EphA2 exosomes relative to the other two cell lines.

Captured EVs were detected with either homo-pairs of proximity probes in a PLA/RCA assay (e.g., CD9/CD9), hetero-pairs (e.g., CD9/CD81), or cocktails comprising CD63, CD81, and CD9 PP1s and CD63, CD81, and CD9 PP2s at either 0.33 μg/mL each or 1 μg/mL each.

Note: 1 μg/mL is the standard concentration for each PP1 and PP2 when assays are performed with a pair of PPs. 0.33 μg/mL was tested to keep the total concentration of PP1s and PP2s in the cocktail equivalent to the standard concentration.

Results are shown in FIG. 20. The signal and background both appear to scale according to the concentration PPs in the cocktail.

Example 2.4.2. Multiplexed Amplified Assays for EVs

Each of the amplified detection methods described in Example 2.4.1 can be applied with multiplexed EV capture on a multispot plate: Single Detection Antibody with RCA; Homo-Pair Proximity Ligation; Hetero-Pair Proximity Ligation; and PLA/RCA Cocktail.

(A). Homo-Pair PLA/RCA Detection on Multiplexed Tetraspanin Capture Array

EVs from a 10-fold dilution of THP-1 cell conditioned medium (CCM) were captured on multispot plates with either a single tetraspanin cAb (CD63, CD81, or CD9) in each well, or all 3 tetraspanin plus isotype control captures multiplexed in each well using the U-PLEX linkers.

Multispot plates were coated using the typical protocol except that the anchor oligonucleotide was also linked to each of the linkers for the spots that were being used and were then added to the antibody mix at 1/9 of the molarity of each the capture antibodies.

EVs were captured for 1 hour. Captured Evs were detected using one of the following homo-pairs: CD63 PP1/CD63 PP2, CD81 PP1/CD81 PP2, CD9 PP1/CD9 PP2 in each well.

Results are shown in FIG. 21A. The multiplex signals were nearly identical to the singleplex signals. This was accomplished by keeping the capture time short and by using the extra blocking step described in Example 2.1.1. This is important when the same capture antibody and detection antibody are used anywhere in the well.

Another assay was performed without the blocking step, and −20% lower signal in the multiplex was observed as compared to the singleplex assays. See FIG. 21B. In this assay, only the CD63/CD63 pair for detection was used.

The CD9/CD63 and CD81/CD63 assays lose signal in the multiplex relative to the singleplex because in the singleplex, there is no CD63 cAb present in the well as interference, whereas in the multiplex, the CD63 capture antibody is present on another spot and can leach off of the surface, causing interference with detection. These assays were performed using the multispot system as described in U.S. Pat. Nos. 10,201,812; 7,842,246 and 6,977,722 (the disclosures of which are hereby incorporated by reference in their entireties). For comparison, a singleplex assay was performed on a plate with a single directly coated CD81 spot, and yielded very similar performance to the corresponding multispot assay.

(B). Cell Line Screening for EV Surface Markers

3 multiplexed capture panels were assembled using the multispot system to display capture antibodies. Biotinylated anchor oligonucleotide was added into each antibody/linker coupling reaction at 1/100th of the concentration (w/v) of the antibody. The stop solution was added, and finally the individual antibody/linker+oligonucleotide/linker reactions were mixed together to form the multiplex.

Panel 1 contained the three tetraspanins and isotype control. Panel 2 contained six proteoglycan surface markers plus the isotype control. Panel 3 contained five cell adhesion proteins and two surface receptors as well as the isotype control.

CCM from 12 cell lines, selected with the expectation of having least one positive for each of the surface markers, were centrifuged for 60 mins at 10,000 g to remove large EVs and cell debris, then captured on each of the panels. Normal serum pools, 10% FBS, and DPBS blanks were included as controls.

1-hour and 4-hour captures were performed for each sample on each panel. Each CCM/panel combination was detected with each of the tetraspanin homo-pairs of PPs using PLA/RCA detection.

Results for selected cell lines for each panel are shown in FIGS. 22A and 22B. Each of the marker/PP pair combinations had low background except for the GPC1, which had a background signal of ˜4000 counts regardless of which PPs were used. This GPC1 antibody was the only polyclonal capture on either panel and appeared to be capturing some component of the PLA/RCA amplification system. Reactivity of each cell line agreed with non-amplified data set run previously, albeit with ˜25-fold signal amplification.

Example 3. Assays for EV “Cargo Proteins”

Measuring the levels of proteins that are inside EVs (i.e., cargo proteins) can be difficult for several reasons. First, many of these proteins are also present outside the EVs in a soluble or aggregated form, sometimes in much higher concentration than in the EV lumen. Thus, a method to separate EV-associated protein from soluble protein is required. Second, the EVs must be lysed to access the cargo proteins. Lysis conditions must be compatible with the assay. Third, some common cargo proteins (e.g., Alix, TSG101) have numerous binding partners that can occlude epitopes or can adopt various conformations that can affect antibody binding.

Typical methods to assess cargo proteins include the following:

Ultracentrifuge purification, with or without density gradient floatation: strength—can produce very pure samples; weaknesses—potential to co-sediment protein aggregates, potential to smash or rupture EV or force aggregation, time-consuming, poor scalability and low yield. Density gradient results in much more pure samples but is very time-consuming.

PEG precipitation: strength—moderately scalable; weaknesses—co-precipitates some proteins, causes aggregation of EVs.

Bead immunoprecipitation: strength—very scalable; weakness—co-elution of non-specifically bound proteins due to high surface area.

Size exclusion chromatography: strength—EVs are not disrupted or aggregated; weaknesses—co-elution of protein aggregates, poor resolution between large proteins and small EVs.

The above methods may be combined with a lysis step, followed by a standard or ultrasensitive MSD assay.

A preferred method for assaying EV cargo is as follows, and illustrated in FIG. 23:

1. Solid-phase immunoprecipitation using a biotinylated capture antibody on a large spot streptavidin plate. As shown in Example 1.1-1.3, nearly all the EVs from a sample can be depleted using one or more of the tetraspanin antibodies.

2. Removal of soluble proteins: wash plate thoroughly, which removes most of the soluble protein from the well. For some proteins, additional treatment such as protease treatment is required (see Example 3.3).

3. Lysis of bound EVs: detergents are used to lyse the captured EVs and solubilize the cargo proteins.

4. Assay: solubilized protein is transferred to a secondary assay plate for standard or ultrasensitive assay.

Example 3.1.1. IL-6 Cargo Measurement in Transfected Expi293 Cell Derived EVs

Expi293 cells were transfected with a plasmid to express a recombinant IL-6/targeting peptide fusion that was designed to target the fusion to the lumen of the exosomes. The targeting vector was purchased from System Biosciences. Cell conditioned medium from wild type and transfected Expi293 cells was lysed with TRITON X-100 and assayed on V-PLEX IL-6 plates.

Results are shown in FIG. 24A. Wild-type Expi293 cells did not secrete measurable levels of IL-6, so any measurable IL-6 was due to the transfection. Transfected cells expressed high levels of IL-6, though the IL-6 was present at high levels outside the exosomes, since the “no-TRITON” condition had high signal.

To determine whether IL-6 was present within the exosomes of the transfected cells, EVs were captured using biotinylated CD63, CD81, CD9, or an isotype control antibody on a large spot streptavidin plate. The plate was then washed, and the captured EVs were lysed with TRITON X-100. The lysate was transferred to a V-PLEX IL-6 plate to assess IL-6.

Results are shown in FIG. 24B. IL-6 appeared to be present within the CD81+ and CD9+ EV populations.

A small fraction of soluble IL-6 in the original sample was expected to non-specifically bind to the large-spot streptavidin plate and then be eluted by the lysis buffer, which may confound the measurement of the exosomal IL-6. To assess this non-specific binding, recombinant IL-6 calibrator was added onto the large-spot capture plate with each of the tetraspanin antibodies. These wells were treated identically to the exosome capture experiment, in that the plate was then washed and lysis buffer was added and transferred to the IL-6 assay plate.

Results are shown in FIG. 24C. All capture antibodies showed similar low levels of non-specific binding. Thus, it is very likely that the enrichment of IL-6 in the CD81 and CD9 captured samples relative to the isotype control is due to IL-6 being inside the EVs. The signal level is expected to be less than 2000 counts if less than 0.05% of the soluble IL-6 was carried over to the assay.

Example 3.1.2. EGFR Cytoplasmic Domain

An ultrasensitive assay for EGFR (cytoplasmic domain) is described. EGFR cytoplasmic domain is not known to be secreted as a soluble protein, thus, most EGFR cytoplasmic domain in cell conditioned medium is expected to be contained in exosomes. The ultrasensitive assay was used to compare levels of EGFR cytoplasmic domain measurable in a cell conditioned medium sample before and after EV lysis. Results in FIG. 25A show that the measurable EGFR cytoplasmic domain increased more than 2-fold after lysis.

EVs from a sample of the same cell conditioned medium was captured using CD63, CD81, CD9, and isotype control antibodies. The captured EVs were then lysed and transferred to the EGFR assay plate. For CD9, nearly all of the EV-associated EGFR signal was recovered (lysed total—unlysed total from FIG. 25A). See FIGS. 25B and 25C.

Example 3.2. Enzymatic “Clean-Up” of Non-Cargo Proteins

In the experiments described in Examples 3.1.1 and 3.1.2, it was possible for some soluble (non-EV cargo) proteins to bind non-specifically to the plate walls or electrode surface in the capture plates and to remain even after thorough washing. Some of this protein may then be released during the lysis step, as the lysis detergent may disrupt the interaction between the non-specifically bound protein and plate surface. Released protein would be transferred along with the solubilized cargo proteins and would lead to an overrepresentation of the amount of cargo protein.

To mitigate this effect, a clean-up method using proteolytic enzymes was developed. Several enzymes were tested, including trypsin, chymotryspin, pepsin, and proteinase K. The desirable qualities for the enzyme were promiscuity, i.e., ability to digest many different proteins, and ease of inhibition, i.e., an enzyme inhibitor was available that would be compatible with the assay.

In this Example, trypsin was used to digest residual soluble HSP70 or IL-6, allowing a more accurate measurement of the levels of HSP70 or IL-6 in the cargo of captured EVs.

The procedure is illustrated in FIG. 26A. The EVs were captured from Expi293 cell conditioned medium on a large spot streptavidin plate coated with either anti-CD81 capture antibody or an isotype control antibody. The samples were then either treated with 1 mg/mL trypsin, 5 mg/mL trypsin, or no enzyme, either before or after the captured EVs were lysed. The resulting lysate/digest was treated with a protease inhibitor to halt the proteolytic activity of the trypsin and then transferred to an assay plate for either HSP70 or IL-6.

Results are shown in FIG. 26B (HSP70) and 26C (IL-6). The signal from the isotype control captured sample is likely due to residual soluble protein since this capture antibody does not capture EVs. For both protein species, the isotype control signal decreased ˜5 fold after enzyme digestion. The signal from the CD81 capture represents the true cargo signal plus the signal due to residual soluble protein. After enzymatic clean-up, most of the soluble protein is digested. Thus, the signal from after enzymatic clean-up represents the true cargo protein level.

Example 3.3. In Situ Measurement of Cargo Proteins

Cargo molecules can be measured in situ in EVs that have been captured on a solid phase, e.g., an antibody coated plate. The EV cargo must be “fixed” to keep it from washing away after the membrane of the EV is permeabilized, similar to immunocytochemistry or intracellular flow cytometry. Previously, it was unknown that EVs can be fixed and permeabilized, since EVs are believed to lack the cytoskeletal proteins that allow cells to retain their structure after fixation.

The procedure is shown in FIG. 27A. Captured EVs were fixed in a 10% solution of formaldehyde in DPBS, then permeabilized with multiple concentrations of TRITON X-100 to partially dissolve the membrane of the EVs.

Results in FIG. 27B show that without permeabilization, no HSP70 is detectable. Without fixation, permeabilization most likely solubilizes most of the cargo proteins, so the detectable HSP70 is very low. After fixation and permeabilization, the HSP70 is detectable. Thus, in principle, cargo proteins can be detected in situ.

Example 4. Read Buffers for Intact EV Assays

All of the MSD standard read buffers contain TRITON X-100 at sufficient concentration to lyse some EVs. Two different read buffers were developed for intact EV assays.

The first read buffer was a mixture of MSD 1× read buffer T with surfactant-free read buffer T to yield a TRITON concentration at 1/10 of the concentration in standard 1× read buffer T. This formulation appears to lyse the EVs very slowly.

The second read buffer was assessed for use with intact EVs. The second read buffer was based on the MSD Read Buffer B. TRITON X-100 was titrated into read buffer B.

Results are shown in FIG. 28. While the signal decreased with increasing TRITON X-100 concentration, no TRITON X-100 was necessary for efficient ECL generation. The surfactant-free formulation generated as much signal as the low levels of TRITON X-100. Tween was added to improve the wetting of the plastic and thus improve the reproducibility of the shape of the air/liquid interface. The addition of Tween increased the signal, likely due to the optical effect, and possible mitigation of trans-dimers and also improved the reproducibility.

Thus, read buffer B with 0.5 mM Tween was determined to be the preferred read buffer for intact EV assays.

Example 4.1. Read Buffers Surfactants for Intact EV Assays

MSD 1× read buffer T and read buffer B containing varying concentrations of TRITON X-100 were tested for performance in an intact EV assay. The EV assay signal change for each buffer type and TRITON X-100 concentration was measured.

Results are shown in FIG. 46. With MSD 1× read buffer T, assay performance improved as the concentration of TRITON X-100 was decreased from 0.1% to 0.01%. The MSD 1× read buffer T assay performance declined as TRITON X-100 concentration was further decreased from 0.01% to 0%. MSD read buffer B with 0.1% TRITON X-100 had low assay performance, while MSD read buffer B with 0% TRITON X-100 had the best assay performance out of all the tested buffer types and TRITON X-100 concentrations.

MSD read buffer A, which contains a surfactant that does not lyse EVs, was tested for assay performance variability. Titration curves using known concentrations of CD81+ EVs were generated for two different lots of MSD read buffer A.

Results are shown in FIG. 47. The two tested lots of MSD read buffer A had very similar titration curves, indicating low lot-to-lot variability in performance.

Example 5. Interpretation of Intact EV Assay Data

Several challenges are present in interpreting EV data. Interpretation of data from intact EV sandwich assays is not as straightforward as for soluble protein analytes. This is because, unlike a soluble analyte assay where the signal generated for a given capture duration is only dependent on the analyte concentration, the signal for intact EVs depends on at least two parameters: the concentration of EVs with the capture moiety (a surface marker); and the total number of copies of the detectable moiety (the capture moiety or a different surface marker) on the captured EVs.

Further, the capture efficiency most likely varies with copy number, i.e., EVs with many copies of a surface marker will be captured more quickly than those with only a few copies.

Diffusion coefficient and thus the capture efficiency depends on the size of the EVs.

When the same marker is used as the capture and detection moiety, there are additional complexities because when the number of copies of the surface marker per EV is low, most (or all) of those copies will be occupied by the capture antibodies and thus will not be detectable. Therefore, at low copy number the signal falls off faster than the copy number.

Example 5.1. Possible Analyses of EVs Based on Two-Marker Assays

In Example 2.2.2, two ways of interpreting data from two-marker intact EV assays were discussed. These methods are useful for making comparisons of EV populations between multiple samples (e.g., cell supernatants or clinical samples) or comparing multiple populations or surface markers within a single sample.

The following types of comparisons can be enabled by using intact EV assays:

1. Compare quantity of EVs with a particular phenotype (surface marker or combination of surface markers) between multiple samples.

Comparison of the quantity of EpCAM+ EVs between samples is exemplified with reference to FIG. 29. In FIG. 29, sample B has very few EpCAM+ EVs relative to other 3 samples. This is ascertained by comparing the EpCAM capture columns of the data tables for each sample. None of the tetraspanin detectors yield appreciable signal for sample B when combined with EpCAM capture. Therefore, very few EVs were captured by the EpCAM capture antibody, indicating a lack of EpCAM+ EVs in this sample. Further, comparison of the quantities of EpCAM+ EVs between samples can determine that sample D has a higher total quantity of EpCAM+ EVs than sample A and C, although it has very few EVs with CD81, so the quantity of EpCAM+CD81+ EVs is lower in sample D than sample A or C.

2. Compare average copy number per EV of particular marker between multiple samples (or total amount of EV associated marker).

Comparison of the level of EV-associated EpCAM between samples is exemplified with reference to FIG. 29. In FIG. 29, sample D has the highest total level of EV-associated EpCAM, determined by summing across the EpCAM detector row.

3. Compare quantity of EVs with one particular surface marker to quantity of EVs with a different surface marker within a given sample.

Referring to FIG. 29, comparison of the quantity of EVs with CD63 to those with CD9 and CD81 in sample D can be performed. By summing each column, the total EV population captured using each surface marker can be compared. CD9+ vesicles are most abundant, and CD81+ vesicles are least abundant.

4. Compare average copy numbers of two or more markers within a given sample.

Referring to FIG. 29, comparison of the relative levels of EV-associated CD63, CD81, CD9, and EpCAM in a particular sample can be performed. By summing across the rows of the tables (constant detection antibody), it was determined that for sample A, the relative levels of CD63, CD81, and CD9 are close to one another, while the level of EV-associated EpCAM is much lower. For sample C, EV-associated CD9 is much higher than the other three markers. For sample D, EV-associated CD63 is relatively low, CD81 is non-existent, but CD9 and EpCAM are both present at similarly high levels.

Example 5.2. Calibrators or Controls

Because the EVs in a biological sample are most likely to be in a heterogeneous population having varying sizes and copy numbers of each surface antigen, it is difficult to have a true calibrator material for intact EV assays in the same manner as for soluble protein assays, wherein each analyte is an identical macromolecule.

However, reference materials, i.e., controls can still be provided. The controls can be actual biologically-derived EVs that are well-characterized, or synthetic materials such as unilamellar vesicles or beads that have similar physiochemical properties as the EVs of interest.

The control material can establish the performance of the assay and provide a reliable sample for normalizing data between plates or experiments and enables correcting for nonlinearity of the assay at the upper and lower ends of the calibration curve. The synthetic materials may be particularly useful, because the surface antigens present can be selected, and the copy number can be tuned to match the biological material of interest, thus functioning as a traditional calibrator.

A useful control material should conform as closely as possible to the size and density of the EVs of interest. Synthetic calibrators have been produced using polymer beads of similar size and density to small EVs and attached tetraspanin proteins to the surface for use as control materials.

Three cell lines have also been selected as particularly efficient at producing EVs: THP-1, Expi293, and HCT-15. See FIG. 30A. The EVs produced by these cell lines have been characterized for use as control material. Nanoparticle tracking analysis was used to quantitate the EVs in the raw material and purified material. FIG. 30B shows the expected size distribution of exosomes, which can be diluted linearly over a wide range in the assays described herein.

Example 6

Cell lines that can be used in this Example include, for example, human cortical neurons differentiated from induced pluripotent stem cells (iPSCs) and from the HCN-2 cell line, and mature astrocytes differentiated from iPSCs and primary human astrocytes. By screening cultured cells from these cell lines, those markers that are overrepresented on either neuronal or astrocyte EVs relative to non-CNS-EVs will be identified for further consideration. For each of these markers, the clone that yields the highest signal and lowest non-specific binding of both the detection antibody and irrelevant EVs will be selected. The sensitivity of each marker will be estimated by comparing the fraction of neuronal or astrocyte-EVs captured by each marker-specific antibody to a tetraspanin cocktail known to capture nearly all EVs. The specificity of each marker will be estimated by comparing the fraction of the off-target population isolated (e.g. astrocyte EVs isolated with proposed neuronal markers). The neuron and astrocyte EVs with at least ten capture antibodies targeting proteins frequently detected on non-CNS EVs (e.g. markers such as PECAM, P-Selectin, EpCAM, E-Cadherin, EphA2, EGFR) will also be screened using tetraspanin detection antibodies. The capture targets will be chosen to represent various sources of non-neuronal EVs, including platelet derived EVs, erythrocyte EVs, endothelial EVs, epithelial EVs. Markers from this screen that are found not to be expressed on either neural or astrocyte EVs will be selected, and a single multiplex panel will be assembled to assess the level of non-CNS EVs in a sample.

Based on the results of the single marker screening, any useful individual markers for capturing either neuronal or astrocyte EVs will be identified. At least a few markers for each cell population will likely be selected for further consideration. All pairwise and triplet combinations of these markers will be assessed using the three-marker assay format shown in FIG. 2. For pairwise combinations, the capture and one of the detection antibodies will be the specific markers while the second detection marker will be a common EV marker or cocktail thereof (e.g. tetraspanins). Pairs will be tested in both orientations. Each combination will be used to assay both neuronal and glial EVs and the specificity will be assessed based on comparing the signal for the non-targeted EV population to the signal for the targeted population. For triplets, all three antibodies will be directed at distinct specific markers and all three orientations will be tested. Combinations that have higher specificity than any individual marker are expected to be identified.

Subject to the results of the single- and multi-marker screening, the most promising individual, pairwise and triplet marker combinations for each target CNS-EV type will be selected. First, the sensitivity of each marker or combination will be tested for capturing pure neuronal or astrocyte EVs isolated from the culture supernatants via ultrafiltration. The selectively captured EV fraction will be assayed in situ using a common EV detector and quantified relative to the total EV population captured by tetraspanin antibody cocktail. Next, a known quantity of neuronal and astrocyte EVs will be spiked into normal human plasma, normal human serum and human CSF. Each of the promising individual markers and combinations will be used for isolation and the EV spike-recovery from each matrix will be assessed by assaying the recovered EVs in situ and comparing to a total EV capture of the same EV sample spiked into clean diluent. For combinations of markers and matrices where spike recovery is high, the spike recovery in EV depleted matrix will be repeated in order to assess whether a fraction of the observed signal was actually due to CNS-EVs native to the matrix which would lead to an overestimation of the spike recovery. Specificity will be further assessed by eluting the recovered EVs and assaying them using the non-CNS-EV panel developed in aim 1. Spike recovery and specificity measurements will also be performed on CNS-EVs recovered using the existing technique practiced in the Kapogiannis Lab (benchmark) for enriching neuronal or astrocyte EVs. It is expected that there are combinations of markers that result in higher specificity for each CNS-EV population than any individual markers.

Any rigorous study of biomarkers must consider biological variables such as sex and the potential for association of these variables with any potential biomarkers. While sex is not expected to be significantly correlated with the surface markers expressed on EVs of the CNS, it will be considered where possible to avoid biasing our screening. In established cell lines, sex will not be considered as a biological variable as there are very few choices for established human cell lines that can be differentiated to functional mature neurons or mature oligodendrocytes (R33 phase). Primary cells from both sexes will be obtained, subject to availability.

Example 7—EV Immunoassays

Intact EV Assays: The basis of the technology in this is example is the sandwich immunoassay with electrochemiluminescence (ECL) detection. This technique is applied by capturing and detecting intact EVs using both common EV markers (e.g. CD81, CD9, CD63) and markers for specific EV populations (e.g. cancer antigens or neuronal markers). Assays for nearly 30 EV surface antigens have been developed, which highlights the ability to rapidly screen antibodies and develop new assays. Up to 10 capture antibodies in each well of a 96 well assay plate can be multiplexed. Combining capture antibody arrays targeting specific EV populations with a common detection antibody or mixture of detection antibodies targeting generic EV markers (like CD81, CD9 and/or CD63) enables the rapid screening of antibody clones for new EV marker discovery and development as well as measurement of multiple EV populations in a single sample. This approach was used to develop assays for EVs bearing L1CAM and NCAM1, two previously reported markers of CNS-EVs in peripheral circulation. L1CAM and NCAM1 antibodies were screened, including specific clones reported in literature as useful in isolating CNS-EVs, against EVs from cell lines known to express each protein. For each protein, a clone was identified that appeared to have higher affinity than the published clones and low non-specific binding of total EVs. These clones were used to assess the fraction of total circulating EVs that were L1CAM+ or NCAM+ as well as to demonstrate good spike recovery of cell-culture derived L1CAM+ and NCAM+ EVs in plasma. The fraction of total EVs bearing neuronal markers (<1%) was considerably lower that what was reported in several published studies (˜10%) and it is concluded that high levels of non-specific binding in the published bead-based isolation techniques may lead to a dramatic overestimation of the EV fraction that are NCAM1+ or L1CAM+.

Ultrasensitive EV Assays: To achieve the sensitivity and specificity needed to reliably measure low-abundance populations of EVs, an ultrasensitive assay format (FIG. 2) was developed based on a variation of proximity ligation amplification. This innovative amplification method generates signal only when two detection antibodies are brought into proximity on the surface of a single captured EV. In practice, after EV capture, two oligonucleotide-labeled detection antibodies directed at distinct molecular targets on the surface of the EVs are added, which mediate the formation and ligation of a circular DNA template and subsequently prime its amplification. A DNA polymerase then creates a long DNA strand covalently linked to one of the antibody-bound oligonucleotides. DNA products are detected using oligonucleotide probes with ECL labels (MSD SULFO-TAG™) and measured using MSD's commercial ECL assay instrumentation. The ultrasensitive assay detection scheme typically yields a 100- to 1000-fold improvement in assay sensitivity versus a sandwich immunoassay and an improvement in specificity due to the use of two distinct detection antibodies58. To demonstrate the requirement that all three antibodies must bind EV proteins in order to generate signal, the antibody at each position was substituted with an irrelevant control antibody and observed nearly a complete loss of signal in each case (FIG. 2B). This technique was used to measure EVs from plasma bearing six different surface proteins (CEA, EGFR, EpCAM, EphA2, mesothelin and transferrin receptor). Signals from EVs in raw plasma vs. EVs purified from the plasma by SEC were similar except for small but consistent signal drops in the SEC samples due to purification yields, indicating that the plasma measurements were truly indicative of the EV population and discriminated against soluble forms of the surface markers.

Example 8

EV cargo proteins were assayed by first capturing the EVs on an immune-capture plate, washing away non-EV associated proteins, then lysing the captured EVs and transferring the lysate to a separate assay well. FIG. 4A demonstrates the application of this concept to measure the cytoplasmic domain of EGFR within captured EVs. For EV cargo targets where non-EV associated levels of the target protein are much higher than the EV-cargo level, the use of a novel protease clean-up method was demonstrated to minimize the amount of soluble protein contamination that may cause inaccurate cargo quantitation. This technique is illustrated for the EV cargo protein HSP70 in FIG. 4B. Briefly, the EVs were captured and washed to remove soluble protein. Protease was added to digest any residual analyte protein that was bound non-specifically in the well. Cargo proteins were protected from digestion by the intact EV membrane. Some of the EVs were released from the surface by digestion of the antibodies but were retained within the well so the assay is not affected. The protease is chemically inactivated, EVs are lysed by detergent and the lysate is transferred to a second plate for the ultra-sensitive assay. The entire process including EV capture, digestion and cargo assay was performed in a single day.

Example 9

To demonstrate the feasibility of the stapling technique CD9 capture antibodies were coupled to the surface of a plate using a pair of short complementary oligonucleotides. A sample of cell-culture derived EVs was selected that was previously shown to have high levels of CD9 and CD81 and low levels of CD63 on their surface and captured these with the CD9 antibodies. The captured EVs were incubated with an ECL-labeled CD9 antibody to render all the captured EVs detectable. Oligo-labeled “stapling” antibodies were added with either CD81, CD63 or an irrelevant control antibody; alternatively, no stapling antibody was added. After amplification by DNA polymerase, the plate was washed in a low salt buffer that enabled the capture antibody oligos to be denatured while the duplex staples, having a higher melting temperature, remained intact. FIG. 1D shows that with CD81 stapling, all the captured EVs were retained, as was expected given the high level of CD81 expression in the sample, while with no stapling ˜80% of the captured EVs were eluted.

CD63 stapling allowed retention of a fraction of the EVs, which is consistent with the low level of EV-associated CD63 in this sample. The irrelevant control antibody also enabled some EV retention, which is likely due to non-specific binding of this antibody to an antigen on the EVs.

Example 10

To demonstrate the EV capture capacity, small EVs (<200 nm diameter) were isolated from a cell line shown to produce high levels of small EVs and concentrated them using ultrafiltration. These EVs were quantified by nanoparticle tracking analysis then added 0.5×10⁹-2×10⁹ EVs to wells of a capture plate coated with anti-CD9 antibodies. After 2 hours, the depleted supernatant was transferred to an assay plate and compared it to fresh, non-depleted supernatant to assess the fraction of EVs remaining unbound. For the most concentrated sample, 93% of the EVs had been depleted and for the least concentrated sample, which was still above the expected concentration of total EVs in blood, over 98% of the EVs were depleted. This strongly supports that capture plates have sufficient capture capacity, particularly for the CNS-EV capture application, where only a small fraction of the total EVs from a biofluid sample are expected to be targeted. It also supports the fact that the majority of EVs can be captured from a sample in a relatively short time (2 hours).

Example 11

This example illustrates that the capture surface in each well has sufficient capacity to capture all the EVs with a given marker. Based on simple geometrical considerations each well of the capture plates should have the capacity to bind at least 2×10⁹ particles with a 100 nm diameter, roughly the average size of exosomes. In a typical 25 uL or 50 uL plasma sample, about 1-2×10⁸ EVs are expected, so capture surface should have sufficient capacity, even if a fraction of the particles are much larger than exosomes. To demonstrate the EV capture capacity, small EVs (<200 nm diameter) were isolated from a cell line shown to produce high levels of small EVs and concentrated them using ultrafiltration. These EVs were quantified by nanoparticle tracking analysis then added 0.5×10⁹-2×10⁹ EVs to wells of a capture plate coated with anti-CD9 antibodies. After 2 hours, the depleted supernatant was transferred to an assay plate and compared it to fresh, non-depleted supernatant to assess the fraction of EVs remaining unbound. For the most concentrated sample, 93% of the EVs had been depleted and for the least concentrated sample, which was still above the expected concentration of total EVs in blood, over 98% of the EVs were depleted. This strongly supports that our capture plates have sufficient capture capacity, particularly for the CNS-EV capture application, where only a small fraction of the total EVs from a biofluid sample was expected to be targeted. It also supports the fact that the majority of EVs can be captured from a sample in a relatively short time (2 hours).

Example 12—Screening Cell Lines for EV Production

In this Example, an EV assay was used to compare EV secretion from various cell lines in different cellular states (e.g., differentiated or undifferentiated), as listed in the left-most column of FIG. 37A. As shown in FIG. 37A, all cell lines secreted detectable levels of CD63+ EVs, demonstrating CD63 as a near-universal EV marker. More variability was observed in the ability of cell lines to express EVs with CD81 or CD9.

Another EV assay was used to compare multiple growth or stimulation conditions on a single cell line, THP-1. FIG. 37B shows the EVs detected from multiple cultures of THP-1 cells, seeded at various densities, and with or without stimulation by phorbol 12-myristate 13-acetate (PMA) to induce differentiation. Culture medium was sample at multiple time points to observe accumulation of EVs over time.

Example 13—Assay Performance in Biofluids

In this Example, EV assay performance was tested in various biofluids. Cell culture-derived EVs were spiked into various clinical matrices (biofluids) of interest, and the biofluids were then subjected to an EV assay to measure for CD9+, CD63+, and CD81+ EVs. Spike levels were chosen to be approximately equivalent to native levels in a diluted sample of the same matrix. FIG. 38 shows the results of the assay with EV-spiked human serum, plasma, CSF, and urine.

Example 14—Additional Two-Marker EV Assays

In this Example, two-marker EV assays were performed on a THP-1 cell line for all combinations of CD63, CD81, and CD9 as capture and detection antibodies. A dilution curve with each of the combinations of CD63, CD81, and CD9 is shown in FIG. 39A. FIG. 39B shows the results of single-marker and two-marker assays for four different cell lines to compare EV subpopulation abundance and relative levels of each EV-associated tetraspanin (i.e., CD63, CD81, and CD9). The relative abundance of EVs bearing each tetraspanin marker in a sample can be estimated by comparing different capture antibodies with the same detection antibody (e.g., as shown in FIG. 39B, many EVs from TT cells, detected by CD9, are captured by CD63, whereas very few are captured by CD81). Relative abundance of each marker on a particular population of EVs can be estimated by comparing different detection antibodies with the same capture antibody (e.g., as shown in FIG. 39B, EVs from Expi293 cells captured with CD63 have low levels of CD63, abundant levels of CD81, and moderate levels of CD9). Abundance of an EV population in multiple samples can be also be compared (e.g., as shown in FIG. 39B, Expi293 cells have the highest abundance of CD81+ EVs, followed by HCT-15 cells, BeWo cells, and lastly TT cells).

Example 15—Additional Two-Marker EV Assays with Biofluids

In this Example, matched human serum and plasma EVs for tetraspanins were tested using single-marker and two-marker EV assays. SEC-purified EVs from matched human serum and plasma from ten healthy donors were assayed with nine combinations of capture and detection antibodies. As shown in FIG. 40, assays that included the marker CD81 as either the capture or detection antibody showed high agreement between matched serum and plasma, most likely because CD81 is not present on platelet-derived EVs and is thus insensitive to variations in phlebotomy and sample handling that affect platelet EV secretion. Conversely, CD63 and CD9 are both abundant on platelet-derived EVs, which are often elevated in plasma relative to serum, depending on post-phlebotomy sample-handling.

Example 16—Singleplex Versus Multiplexed Assays

In this Example, the performance of singleplex and multiplex EV assays were compared. EVs from a THP-1 cell line were assayed using all combinations of CD63, CD81, and CD9 as capture and detection antibodies, using both singleplex and multiplex formats. In addition, an isotype-matched negative control antibody was included to estimate the non-specific binding of EVs to the antibody-coated spots. Each capture antibody was also combined with a cocktail of all three detection antibodies. Results in FIG. 41 show that in all cases, the singleplex and multiplex assays produce equivalent measurements of EVs in the sample.

Example 17—Developing EV Screening Panels

This Example describes development of a new EV screening panel using a multiplex format, which facilitates comparison of multiple capture antibodies targeting the same markers and enables rapid screening for preferred antibodies in an assay. Several cell lines known to express CD4 were selected, and several cell lines known not to express CD4 were chosen as negative controls. Multiple anti-CD4 antibodies were present in each well of a multiplex assay plate. Conditioned medium from each cell line was precleared by centrifugation to remove cell debris, and cleared supernatant was added to each well. Captured EVs were detected with a combination of CD63, CD81, and CD9 detection antibodies in order to maximize detection signal. As shown in FIG. 42A, of the four clones tested, “clone D” yielded the highest signal in all the expected positive cell lines and the lowest or equivalent signal in the negative cell lines and controls. Thus, clone D was selected as the preferred antibody for capturing CD4+ EVs. This screening process was performed for the cell surface markers shown in FIG. 42B.

Example 18—Screening of Culture Conditioned Media

In this Example, EVs were captured from cell conditioned medium using the antibody panels described in Example 17 and shown in FIG. 42B. Captured EVs were detected with a combination of CD63, CD81, and CD9. FIGS. 43A and 43B show the ratio between the background-subtracted ECL signal on each specific capture spot and the negative control antibody spot in the same well, which enabled identification of samples producing EVs bearing each of the target surface markers. Light gray-highlighted cells had ratio greater than five-fold, and dark gray-highlighted cells had ratio greater than ten-fold.

Example 19—Screening of Human Biofluid Samples

In this Example, human biofluids were screened for EVs using the antibody panels described in Example 17 and shown in FIG. 42B. Captured EVs were detected with a combination of CD63, CD81, and CD9. FIG. 44 shows the ratio between the background-subtracted signal on each specific capture spot and the negative isotype-control spot in the same well which enabled identification of samples producing EVs bearing each of the target surface markers. Light gray-highlighted cells had ratio greater than five-fold, and dark gray-highlighted cells had ratio greater than ten-fold. Twenty-three of the 45 markers were detectable in one or more of the different types of human biofluid samples tested.

Example 20—Analysis of EV Screening Data

Hierarchical clustering analysis was performed on the cell line and human biofluid EV screening data from Examples 18 and 19 (and corresponding FIGS. 43A-43B and FIG. 44). Results in FIG. 45 show that epithelial cell lines form one cluster, while a second cluster includes all the leukocytes and endothelial cells. All of the human biofluids clustered with the leukocytes.

Example 21—Multi-Marker Screening with Complex Screening Pools

For large antibody-conjugate pools, or large numbers of samples, a high-throughput sequencing platform will be needed to obtain sufficient sequencing counts to observe the low frequency triplets formed from combinations of low-abundance markers. For these experiments, libraries will be prepared and sequenced using a next-generation sequencing platform. The estimated dynamic range will tolerate between the least and most abundant markers for a given number of sequencing reads available in our surface signature approach. Only those markers that are present on nearly every EV (≥95%) of a given population will be determined, and the number of copies (k) of a marker on individual EVs is expected to follow a Poisson distribution: P(k)=e(λ^(k))/k!, where λ, is the average number of copies of the marker per EV. Thus, only markers where λ≥3 are considered to ensure P(0)<5%, i.e. if ≥95% of the EVs to have at least 1 copy of a given marker is desired, the average number of copies of that marker must be at least 3, based on Poisson statistics.

There has been no definitive measure of the number of total surface proteins per EV. However, based simply on geometry, if 10% of the surface area on each 100 nm EV were occupied by the proteins targeted by antibodies in a screening pool (˜300 protein molecules), the least abundant markers to be detected (λ≥3) would represent 1% of these total proteins and a combination of three of these “low abundance markers” would account for 1 read in 106 (0.013). To avoid missing these low abundance events due to sequencer sampling noise, several million reads would be required, which is readily achievable using modern sequencing technology. In reality, this is likely an overestimation of the sequencing depth needed since the surface area of EVs occupied by targeted proteins is likely less than 10%, particularly since highly abundant and common EV proteins, such as the tetraspanins, would be excluded from the screening pools as they would be unlikely to provide specificity. In the unlikely event that one or a few particular highly abundant proteins account for all of the reads in a sequencing run but do not yield cell type specificity, these would be removed from the screening pool and the experiment re-run to provide the depth to observe the less abundant markers.

To illustrate the advanced capability of the multi-marker screening technique, a higher complexity screening pool will be used to identify multi-marker EV signatures in 5 cell types that secrete relatively high levels of EVs into blood: monocytes, vascular endothelium, B-Cells, CD4+T-cell and CD8+ T-cells, as well as platelets, which are a common source of contaminating EVs in blood. This will demonstrate the ability of the technique to identify and discriminate signatures between EVs secreted by closely related cell populations (e.g. CD4 and CD8 T-cells). When working with new assay targets, multiple antibody clones for the same target marker are often included, to identify the highest affinity clone. In a screening conjugate pool, these will compete with one another and the most represented barcodes will indicate the highest affinity clone for each target. A screening pool will be generated using ˜60 antibodies, with up to 3 clones against each of at least 20 surface marker targets, to create ˜180 uniquely barcoded conjugates. At least 4 target markers for each of the cell types will be selected based on previous studies and publications. EVs from at least two cell lines representing each cell type, likely including THP-1, HL-60, Ramos, GA-10, Jurkat, Molt-4 and HUVEC, plus primary cells from ATCC for each type will be assayed using the antibody pool to generate one sequencing library per sample. Individual sample types will receive identifying sample barcodes during installation of sequencing adaptors. The ˜18 sample libraries will be normalized, combined, and sequenced in a single next generation sequencing run, which should yield ˜1M reads per sample. Selecting specific multi-marker signatures for EVs of a given cell type will require selecting combinations of two or three markers that are well represented in each of the samples for the given cell type while being absent or poorly represented in the samples for all other cell types. There may be multiple 3-marker combinations that define a cell type. These would need to be tested in the actual isolation protocols described below to determine which has the highest specificity and recovers the greatest number of vesicles from the relevant population. Thus, while this technique will be most useful when some prior knowledge of the likeliest useful surface markers is available, the method could make unbiased screening possible for new cell types by using very large libraries of antibody-conjugates. 

What is claimed is:
 1. A method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: a. contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; b. binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; c. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.
 2. A method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: a. contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV and the binding reagent; b. binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; c. hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; and d. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.
 3. A method of isolating an extracellular vesicle (EV) of interest in a sample, comprising: a. contacting the sample with a surface and selectively binding the EV of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; b. hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; and c. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.
 4. The method of any of claims 1-3, further comprising assaying the EV of interest.
 5. The method of claim 2, further comprising contacting a detection oligonucleotide with the surface, wherein the oligonucleotide is complementary to the amplicon.
 6. The method of claim 5, wherein the detection oligonucleotide is detectably labeled.
 7. The method of any of claims 1-3, further comprising releasing the EV of interest from the surface.
 8. The method of claim 7, further comprising assaying the EV of interest.
 9. The method of any of claims 1-3, wherein the eluting unwanted components of the sample from the surface comprises washing the surface with a washing solution.
 10. The method of claim 9, wherein the unwanted components are soluble in the washing solution or are unwanted EVs.
 11. The method of any of claims 1-10, wherein the capture reagent is releasably bound to the surface by a labile linker.
 12. The method of claim 11, wherein the labile linker is a heat-labile, a photolabile, or a chemically labile linker.
 13. The method of claim 11, wherein the labile linker is an oligonucleotide that is complementary to an oligonucleotide bound to the surface or is an oligonucleotide comprising a restriction site cleavable by a restriction endonuclease.
 14. The method of claim 11, wherein the releasing the capture reagent from the surface comprises denaturing the labile linker.
 15. The method of claim 11, wherein the releasing the capture reagent from the surface comprises cleaving the labile linker.
 16. The method of claim 7, wherein the releasing the EV from the surface comprises denaturing the anchoring oligonucleotide and amplicon.
 17. The method of any of claims 1-16, wherein the bound anchoring reagent and binding agent, or the hybridized anchoring oligonucleotide and amplicon is stable during the release of the capture reagent from the surface.
 18. The method of any of claims 1-16, wherein the hybridized linker oligonucleotide, tag oligonucleotide and anchoring oligonucleotide are stable during the release of the capture reagent from the surface.
 19. The method of any of claims 3-15 and 18, wherein the linker oligonucleotide comprises a first region complementary to the tag nucleotide of about 15 to 35 oligonucleotides and a second region complementary to the anchoring nucleotide of about 15 to 35 oligonucleotides.
 20. The method of claim 19, wherein the first and second regions are each 20-30 oligonucleotides.
 21. The method of any of claims 1-20, wherein the capture reagent binds to a first surface marker on the EV and the binding reagent binds to a second surface marker on the EV.
 22. The method of claim 21, wherein the unwanted components comprise an EV that does not have the second surface marker.
 23. The method of claim 21, wherein the first or second surface marker is common to substantially all EVs.
 24. The method of claim 23, wherein the first marker is common to EVs.
 25. The method of claim 24, wherein the marker is a tetraspanin.
 26. The method of claim 25, wherein the tetraspanin is CD9, CD63, or CD81.
 27. The method of any of claims 1-26, wherein at least one of the capture reagent or binding reagent is an antibody to a disease-specific target molecule in or on the surface of the EV.
 28. The method of any of claims 21-27, wherein at least one of the first or second surface marker is specific to a central nervous system (CNS) EV.
 29. The method of claim 28, wherein the first or second surface marker is specific to a neuron EV, an astrocyte EV, an oligodendrocyte EV, or a microglia EV.
 30. The method of claim 29, wherein the first or second surface marker is specific to a neuron EV.
 31. The method of claim 30, wherein the first or second surface marker specific to a neuron EV is L1CAM, NCAM, NRCAM, CHL1, Glu-R2, neurofascin, DAT1, CD90, CD24, or synaptophysin.
 32. The method of claim 30, wherein the neuron EV is a dopaminergic neuron, a GABAergic neuron, a cholinergic neuron, a serotonergic neuron, or a glutamatergic neuron.
 33. The method of claim 29, wherein the first or second surface marker is specific to an astrocyte EV.
 34. The method of claim 33, wherein the first or second surface marker specific to an astrocyte EV is ALDH1L1, GLT-1, GLAST, CD184, CD44, A2B5, CD80, or CD86.
 35. The method of claim 29, wherein the first or second surface marker is specific to an oligodendrocyte EV.
 36. The method of claim 35, wherein the first or second surface marker specific to an oligodendrocyte EV is O4, PDGFRa, CSPG4 (NG2, MCSP), GD3, MOG, or MBP.
 37. The method of claim 29, wherein the first or second surface marker is specific to a microglia EV.
 38. The method of claim 37, wherein the microglia EV is Tmem119, CD11bF4/80, CD68, P2RY12, or CXC3R1.
 39. The method of claim 21, wherein the first or second surface marker is specific to an Alzheimer's biomarker.
 40. The method of any of claims 1-39, wherein the EV is an exosome, a micro-vesicle, or a large-oncosome.
 41. The method of claim 2, further comprising binding the EV to from two to ten binding reagents, wherein at least one binding reagent comprises an amplification primer oligonucleotide, wherein the primer oligonucleotide binds to the circular oligonucleotide template.
 42. The method of any of claims 1-41, wherein the EV is secreted from a cell of the central nervous system (CNS).
 43. The method of claim 42, wherein the cell of the CNS is a neuron, an astrocyte, an oligodendrocyte, or microglia.
 44. The method of any of claims 1-43, wherein the EV encapsulates a protein, a nucleic acid, a lipid, or a combination thereof.
 45. The method of claim 44, wherein the EV encapsulates an RNA.
 46. A method of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV of interest in a sample, comprising: a. contacting the sample comprising the EV with a surface, wherein the EV encapsulates the protein, nucleic acid, lipid, or combination thereof, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; and (ii) a binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; b. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and c. conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof.
 47. A method of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV of interest in a sample, comprising: a. contacting the sample comprising the EV with a surface, wherein the EV encapsulates the protein, nucleic acid, lipid, or combination thereof, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; (ii) a binding reagent, wherein the binding reagent comprises a primer oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; b. binding a circular oligonucleotide template to the primer oligonucleotide to form an amplicon by rolling circle amplification, wherein the amplicon comprises a sequence that is complementary to the anchoring oligonucleotide; c. hybridizing the anchoring oligonucleotide to the amplicon to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and anchoring oligonucleotide; d. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and e. conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof.
 48. A method of identifying, quantitating, or both, a protein, a nucleic acid, a lipid, or a combination thereof, encapsulated by an EV in a sample, comprising: a. contacting the sample comprising the EV with a surface, wherein the EV encapsulates the protein, nucleic acid, lipid, or combination thereof, and selectively binding the EV to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring oligonucleotide; (ii) a binding reagent, wherein the binding reagent comprises a tag oligonucleotide, thereby forming a complex on the surface comprising the capture reagent, the EV, and the binding reagent; b. hybridizing a linker oligonucleotide to the tag oligonucleotide and to the anchoring oligonucleotide to form a second complex on the surface comprising the capture reagent, the EV, the binding reagent, and the anchoring oligonucleotide; c. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest; and d. conducting an assay to identify, quantitate, or both, the encapsulated protein, nucleic acid, lipid, or combination thereof.
 49. The method of any of claims 46-48, wherein the EV encapsulates a protein, wherein the protein is TSG101, HSP70, ALIX/PDCD6IP, Flotillin-1, Tuj 1, Tyr hydroxylase, NSE, NF-L, GFAP, S100β, GluSyn, CNPase, Oligo2, TMEM119, Tau, phospho-Tau-181 or a combination thereof.
 50. The method of claim 47, wherein the EV encapsulates a protein, wherein the protein is TSG101, HSP70, ALIX/PDCD6IP, Flotillin-1, or a combination thereof.
 51. The method of any of claims 46-48, wherein the assay comprises contacting the surface with a protease, inactivating the protease, lysing the EV and transferring the lysate to a second surface, wherein the lysate is detected using an assay.
 52. The method of claim any of claims 1-51, wherein the sample comprises EVs produced from a cell differentiated from a cell-line, differentiated from an induced pluripotent stem cell, a primary cell, or a combination thereof.
 53. The method of any of claims 1-51, wherein the sample is a mammalian fluid, secretion, or excretion.
 54. The method of any of claims 1-51, wherein the sample is a purified mammalian fluid, secretion, or excretion.
 55. The method of claim 53 or 54, wherein the mammalian fluid, secretion, or excretion is whole blood, plasma, serum, sputum, lachrymal fluid, lymphatic fluid, synovial fluid, pleural effusion, urine, sweat, cerebrospinal fluid, ascites, milk, stool, bronchial lavage, saliva, amniotic fluid, nasal secretions, vaginal secretions, a surface biopsy, sperm, semen/seminal fluid, wound secretions, and excretions.
 56. The method of claim 55, wherein the sample is cerebrospinal fluid.
 57. The method of claim 55, wherein the sample is plasma.
 58. The method of claim 55, wherein the sample is serum.
 59. The method of claim 54, wherein the mammalian fluid, secretion, or excretion is purified by differential centrifugation, ultrafiltration, size-exclusion chromatography, immuno-affinity, or a combination thereof.
 60. The method of any of claims 1-59, wherein the sample comprises purified EVs.
 61. The method of any of claims 1-60, wherein the capture reagent comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer.
 62. The method of any of claims 1-61, wherein the binding reagent comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer.
 63. The method of any of claims 1-60, wherein the capture reagent and the binding reagent comprise antibodies to a target molecule in or on the surface of the EV.
 64. The method of claim 2 or 47, wherein the amplicon further comprises one or more detection sequences and the measuring step further comprises contacting the extended sequence with a plurality of labeled probes complementary to the one or more detection sequences.
 65. The method of claim 2 or 47, wherein the amplicon remains localized on the surface following the amplification.
 66. The method of claim 2 or 47, wherein the amplicon remains bound to the surface after the amplification.
 67. The method of claim 2 or 47, wherein the amplicon is bound to the anchoring reagent at a position within 10 μm, 5 μm, or 100 nm of the location of the complex on the surface.
 68. A kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: a. a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring reagent; b. a binding reagent for the EV.
 69. A kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: a. a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring oligonucleotide sequence; b. a binding reagent for the EV that is linked to a primer oligonucleotide; and c. a circular oligonucleotide template comprising a sequence complementary to the primer oligonucleotide.
 70. A kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: a. a surface comprising (i) a capture reagent for the EV, wherein the capture reagent is releasably bound to the surface, and (ii) an anchoring oligonucleotide; b. a binding reagent for the EV that is linked to a tag oligonucleotide; and c. a linker oligonucleotide comprising (i) a sequence complementary to the tag oligonucleotide, and (ii) a sequence complementary to the anchoring oligonucleotide.
 71. The kit of any of claims 68-70, wherein the capture reagent comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or aptamer.
 72. The kit of any of claims 68-71, wherein the binding reagent comprises an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or aptamer.
 73. The kit of any of claims 68-72, wherein the surface comprises a particle.
 74. The kit of any of claims 68-73, wherein the surface comprises a well of a multi-well plate.
 75. The kit of any of claims 68-74, wherein the surface comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent or anchoring oligonucleotide are located on two distinct binding domains on the surface.
 76. The kit of claim 74, wherein the well comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent or anchoring oligonucleotide are located on two distinct binding domains within the well.
 77. The kit of claim 75 or 76, wherein the surface comprises a plurality of distinct binding domains and the capture reagent and the anchoring oligonucleotide are located on the same binding domain on the surface.
 78. The kit of claim 74, wherein the well comprises a plurality of distinct binding domains and the capture reagent and the anchoring reagent or anchoring oligonucleotide are located on the same binding domain within the well.
 79. The kit of any of claims 68-78, wherein the capture reagent and the anchoring reagent or anchoring oligonucleotide are within 10 μm, 5 μm, or 100 nm on the surface.
 80. The kit of claim any of claims 68-79, wherein the surface comprises an electrode.
 81. The kit of any of claims 68-80, wherein the capture reagent binds a common EV surface protein selected from CD9, CD63, or CD81.
 82. The method of any of claims 46-48, wherein the assay is an ultrasensitive assay.
 83. The method of claim 82, wherein the ultrasensitive assay is proximity ligation amplification (PLA) or proximity ligation amplification using rolling circle amplification (PLA-RCA).
 84. A method of isolating an EV of interest in a sample, comprising: a. contacting the sample with a surface, and selectively binding the EV of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences; (ii) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent, and b. binding the anchoring reagent to the second binding reagent, wherein the anchoring reagent is bound to the second binding reagent by an adaptor oligonucleotide, wherein the adaptor oligonucleotide comprises (1) a nucleotide sequence complementary to a nucleotide sequence of the anchoring reagent, and (2) a nucleotide sequence complementary to a nucleotide sequence of the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV and the first and second binding reagents; and c. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.
 85. The method of claim 84, wherein the capture reagent is releasably bound to the surface by an oligonucleotide comprising a first cleavage site and wherein the adaptor oligonucleotide comprises a second cleavage site.
 86. The method of claim 84 or 85, wherein said surface is a bead or a planar substrate having multiple binding sites.
 87. The method of any of claims 84 to 86, wherein the sample comprises at least two EVs of interest and the surface comprises at least a first bead and a second bead, wherein a first capture reagent releasably bound to the first bead binds to a first EV and a second capture reagent releasably bound to the second bead binds to a second EV.
 88. The method of claims 84 to 86, wherein the sample comprises at least two EVs of interest and the surface comprises at least a first region and a second region, wherein a first capture reagent releasably bound to the first region binds to a first EV and a second capture reagent releasably bound to the second region binds to a second EV.
 89. A method of isolating an EV of interest in a sample, comprising: a. contacting the sample with, and selectively binding the EV of interest to: (i) first and second binding reagents, wherein the first binding reagent and the second binding reagent comprise complementary nucleotide sequences; (ii) a capture reagent, wherein the capture reagent is linked to an anchoring reagent, wherein the anchoring reagent comprises: (1) a nucleotide sequence complementary to the second binding reagent nucleotide sequence and (2) at least one cleavage site, and wherein the anchoring reagent is bound to a surface, and b. hybridizing the anchoring reagent with the second binding reagent, thereby forming a complex on the surface comprising the capture reagent, the EV, and the first and second binding reagents; and c. releasing the anchoring reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the EV of interest.
 90. The method of claim 89, wherein the anchoring reagent comprises biotin, and the surface comprises streptavidin.
 91. The method of any one of claims 89 to 90, wherein the anchoring reagent comprises two cleavage sites.
 92. The method of any one of claims 89 to 91, wherein the cleavage site is a restriction site.
 93. The method of claim 89 or 90, wherein the capture reagent is linked to the anchoring reagent with PEG, poly(A), or a polynucleotide sequence.
 94. A method of determining extracellular vesicle (EV) surface markers, comprising contacting the EV with a plurality of unique binding reagents, wherein each unique binding reagent comprises a detection sequence comprising a unique barcode oligonucleotide sequence, wherein if at least three unique binding reagents bind to three unique EV surface markers, an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the three unique binding reagents, and wherein the output oligonucleotide is capable of being sequenced to identify the three unique EV surface markers.
 95. A method of determining extracellular vesicle (EV) surface markers, comprising: a. contacting the EV with a plurality of unique binding reagents, wherein each unique binding reagent comprises a detection sequence comprising a unique barcode oligonucleotide sequence, wherein if at least three unique binding reagents bind to three unique EV surface markers, an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the three unique binding reagents; and b. sequencing the output oligonucleotide to identify the barcode oligonucleotide sequences, thereby determining the at least three unique EV surface markers.
 96. The method of claim 89, wherein at least one of the plurality of binding reagents comprises a detection sequence that comprises a hybridization sequence that is complementary to at least a portion of the detection oligonucleotide sequence of at least one other binding reagent.
 97. The method of claim 89 or 90, wherein the plurality of binding reagents comprises: a. a first binding reagent comprising a first detection sequence that comprises a first hybridization sequence, and a first amplification primer site; b. a second binding reagent comprising a second detection sequence that comprises a second hybridization sequence, and a third hybridization sequence; and c. a third binding reagent comprising a third detection sequence that comprises a fourth hybridization sequence, and a second amplification primer site, wherein the first hybridization sequence and the second hybridization sequence are complementary; wherein the third hybridization sequence and the fourth hybridization sequence complementary; and wherein generating the single output oligonucleotide comprises ligating, amplifying, or both, the hybridized first detection sequence, second detection sequence, and third detection sequence.
 98. The method of any of claims 89-91, wherein the plurality of unique binding reagents comprises at least ten unique binding reagents.
 99. The method of any one of claims 89 to 92, wherein the plurality of unique binding reagents comprises about 10 to about 100 unique binding reagents.
 100. The method of any one of claims 89 to 93, wherein the sequencing is performed by next-generation sequencing.
 101. The method of any one of claims 89 to 94, wherein sequencing the output oligonucleotide comprises: adding one or more sequencing primers to the single output oligonucleotide; and sequencing the single output oligonucleotide using the sequencing primers.
 102. The method of any of claims 89 to 95, wherein the multiplexed method is conducted in solution.
 103. A method of screening EV capture reagents and binding reagents, comprising: a. contacting a sample comprising an EV with: (i) a first binding reagent comprising a first unique barcode sequence and a second binding reagent comprising a second unique barcode sequence, wherein the first and second binding reagent comprise complementary nucleotide sequences; and (ii) a capture reagent, wherein the capture reagent is linked to an anchoring reagent, wherein the anchoring reagent comprises a third unique barcode sequence, wherein the anchoring reagent comprises a nucleotide sequence complementary to the second binding reagent nucleotide sequence, wherein the anchoring reagent is releasably bound to the surface, wherein if the EV binds to the capture reagent and the first and second binding reagents, then an output oligonucleotide is generated that comprises the barcode oligonucleotide sequences of each of the capture reagent, and the first and second binding reagents; and b. sequencing the output oligonucleotide to identify the barcode oligonucleotide sequences, thereby determining the at least three unique EV surface markers.
 104. The method of claim 103, wherein the first binding reagent further comprises a first amplification primer, and the anchoring reagent further comprises a second amplification primer.
 105. The method of claim 103 or 104, wherein the anchoring reagent further comprises at least one cleavage site.
 106. The method of claim 105, wherein the at least one cleavage site is a restriction site.
 107. The method of any of claims 103-106, wherein the capture reagent is linked to the anchoring reagent with PEG, poly(A), or a polynucleotide sequence.
 108. A composition comprising an EV and three unique binding reagents, wherein the three unique binding reagents are bound to three unique EV surface markers.
 109. A method of isolating a surface marker displaying agent of interest in a sample, comprising: a. contacting the sample with a surface and selectively binding the surface marker displaying agent of interest to: (i) a capture reagent releasably bound to the surface, wherein the surface further comprises an anchoring reagent; and (ii) a binding reagent; b. binding the anchoring reagent to the binding reagent, thereby forming a complex on the surface comprising the capture reagent, the surface marker displaying agent and the binding reagent; c. releasing the capture reagent from the surface and eluting unwanted components of the sample from the surface, thereby isolating the surface marker displaying agent of interest.
 110. The method of claim 109, wherein the surface marker displaying agent is a cell, a virus or viral particle, an organelle, a vesicle, or combination thereof.
 111. The method of claim 110, wherein the surface marker displaying agent is a viral particle.
 112. A kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: a. a surface comprising a binding domain; b. a linking reagent capable of binding to the binding domain; and c. an anchoring reagent capable of binding to the binding domain.
 113. The kit of claim 112, further comprising a capture reagent, wherein the capture reagent is capable of binding to the linking reagent.
 114. A kit for detecting an EV in a sample comprising, in one or more vials, containers, or compartments: a. a surface comprising a targeting reagent complement in a binding domain; b. a linking reagent connected to a targeting reagent, wherein the targeting reagent is a binding partner of the targeting reagent complement; and c. an anchoring reagent comprising a supplemental linking reagent, wherein the supplemental linking reagent is capable of binding to the linking reagent.
 115. The kit of claim 114, further comprising: a capture reagent for a surface marker, wherein the capture reagent comprises a supplemental linking reagent capable of binding to the linking reagent.
 116. The kit of claim 114 or 115, wherein the surface comprises a plurality of binding domains, wherein each binding domain comprises a different targeting reagent complement; and wherein the kit further comprises a plurality of linking reagents, each linking reagent connected to a different targeting reagent for each of the different targeting reagent complements.
 117. The kit of any one of claims 112 to 116, wherein the anchoring reagent comprises BSA. 